lvmraid(7) — Linux manual page

NAME | DESCRIPTION | USAGE | DEVICE FAILURE | DATA INTEGRITY | RAID1 TUNING | RAID TAKEOVER | RAID RESHAPING | RAID5 VARIANTS | RAID6 VARIANTS | HISTORY | SEE ALSO | COLOPHON

LVMRAID(7)                                                    LVMRAID(7)

NAME         top

       lvmraid — LVM RAID

DESCRIPTION         top

       lvm(8) RAID is a way to create a Logical Volume (LV) that uses
       multiple physical devices to improve performance or tolerate
       device failures.  In LVM, the physical devices are Physical
       Volumes (PVs) in a single Volume Group (VG).

       How LV data blocks are placed onto PVs is determined by the RAID
       level.  RAID levels are commonly referred to as 'raid' followed
       by a number, e.g.  raid1, raid5 or raid6.  Selecting a RAID level
       involves making tradeoffs among: physical device requirements,
       fault tolerance, and performance.  A description of the RAID
       levels can be found at
       www.snia.org/sites/default/files/SNIA_DDF_Technical_Position_v2.0.pdf

       LVM RAID uses both Device Mapper (DM) and Multiple Device (MD)
       drivers from the Linux kernel.  DM is used to create and manage
       visible LVM devices, and MD is used to place data on physical
       devices.

       LVM creates hidden LVs (dm devices) layered between the visible
       LV and physical devices.  LVs in the middle layers are called sub
       LVs.  For LVM raid, a sub LV pair to store data and metadata
       (raid superblock and write intent bitmap) is created per raid
       image/leg (see lvs command examples below).

USAGE         top

       To create a RAID LV, use lvcreate and specify an LV type.  The LV
       type corresponds to a RAID level.  The basic RAID levels that can
       be used are: raid0, raid1, raid4, raid5, raid6, raid10.

       lvcreate --type RaidLevel [OPTIONS] --name Name --size Size VG
       [PVs]

       To display the LV type of an existing LV, run:

       lvs -o name,segtype LV

       (The LV type is also referred to as "segment type" or "segtype".)

       LVs can be created with the following types:

   raid0
       Also called striping, raid0 spreads LV data across multiple
       devices in units of stripe size.  This is used to increase
       performance.  LV data will be lost if any of the devices fail.

       lvcreate --type raid0 [--stripes Number --stripesize Size] VG
       [PVs]

       --stripes Number
              specifies the Number of devices to spread the LV across.

       --stripesize Size
              specifies the Size of each stripe in kilobytes.  This is
              the amount of data that is written to one device before
              moving to the next.

       PVs specifies the devices to use.  If not specified, lvm will
       choose Number devices, one for each stripe based on the number of
       PVs available or supplied.

   raid1
       Also called mirroring, raid1 uses multiple devices to duplicate
       LV data.  The LV data remains available if all but one of the
       devices fail.  The minimum number of devices (i.e. sub LV pairs)
       required is 2.

       lvcreate --type raid1 [--mirrors Number] VG [PVs]

       --mirrors Number
              specifies the Number of mirror images in addition to the
              original LV image, e.g. --mirrors 1 means there are two
              images of the data, the original and one mirror image.

       PVs specifies the devices to use.  If not specified, lvm will
       choose Number devices, one for each image.

   raid4
       raid4 is a form of striping that uses an extra, first device
       dedicated to storing parity blocks.  The LV data remains
       available if one device fails.  The parity is used to recalculate
       data that is lost from a single device.  The minimum number of
       devices required is 3.

       lvcreate --type raid4 [--stripes Number --stripesize Size] VG
       [PVs]

       --stripes Number
              specifies the Number of devices to use for LV data.  This
              does not include the extra device lvm adds for storing
              parity blocks.  A raid4 LV with Number stripes requires
              Number+1 devices.  Number must be 2 or more.

       --stripesize Size
              specifies the Size of each stripe in kilobytes.  This is
              the amount of data that is written to one device before
              moving to the next.

       PVs specifies the devices to use.  If not specified, lvm will
       choose Number+1 separate devices.

       raid4 is called non-rotating parity because the parity blocks are
       always stored on the same device.

   raid5
       raid5 is a form of striping that uses an extra device for storing
       parity blocks.  LV data and parity blocks are stored on each
       device, typically in a rotating pattern for performance reasons.
       The LV data remains available if one device fails.  The parity is
       used to recalculate data that is lost from a single device.  The
       minimum number of devices required is 3 (unless converting from 2
       legged raid1 to reshape to more stripes; see reshaping).

       lvcreate --type raid5 [--stripes Number --stripesize Size] VG
       [PVs]

       --stripes Number
              specifies the Number of devices to use for LV data.  This
              does not include the extra device lvm adds for storing
              parity blocks.  A raid5 LV with Number stripes requires
              Number+1 devices.  Number must be 2 or more.

       --stripesize Size
              specifies the Size of each stripe in kilobytes.  This is
              the amount of data that is written to one device before
              moving to the next.

       PVs specifies the devices to use.  If not specified, lvm will
       choose Number+1 separate devices.

       raid5 is called rotating parity because the parity blocks are
       placed on different devices in a round-robin sequence.  There are
       variations of raid5 with different algorithms for placing the
       parity blocks.  The default variant is raid5_ls (raid5 left
       symmetric, which is a rotating parity 0 with data restart.)  See
       RAID5 VARIANTS below.

   raid6
       raid6 is a form of striping like raid5, but uses two extra
       devices for parity blocks.  LV data and parity blocks are stored
       on each device, typically in a rotating pattern for performance
       reasons.  The LV data remains available if up to two devices
       fail.  The parity is used to recalculate data that is lost from
       one or two devices.  The minimum number of devices required is 5.

       lvcreate --type raid6 [--stripes Number --stripesize Size] VG
       [PVs]

       --stripes Number
              specifies the Number of devices to use for LV data.  This
              does not include the extra two devices lvm adds for
              storing parity blocks.  A raid6 LV with Number stripes
              requires Number+2 devices.  Number must be 3 or more.

       --stripesize Size
              specifies the Size of each stripe in kilobytes.  This is
              the amount of data that is written to one device before
              moving to the next.

       PVs specifies the devices to use.  If not specified, lvm will
       choose Number+2 separate devices.

       Like raid5, there are variations of raid6 with different
       algorithms for placing the parity blocks.  The default variant is
       raid6_zr (raid6 zero restart, aka left symmetric, which is a
       rotating parity 0 with data restart.)  See RAID6 VARIANTS below.

   raid10
       raid10 is a combination of raid1 and raid0, striping data across
       mirrored devices.  LV data remains available if one or more
       devices remains in each mirror set.  The minimum number of
       devices required is 4.

       lvcreate --type raid10
              [--mirrors NumberMirrors]
              [--stripes NumberStripes --stripesize Size]
              VG [PVs]

       --mirrors NumberMirrors
              specifies the number of mirror images within each stripe.
              e.g.  --mirrors 1 means there are two images of the data,
              the original and one mirror image.

       --stripes NumberStripes
              specifies the total number of devices to use in all raid1
              images (not the number of raid1 devices to spread the LV
              across, even though that is the effective result).  The
              number of devices in each raid1 mirror will be
              NumberStripes/(NumberMirrors+1), e.g. mirrors 1 and
              stripes 4 will stripe data across two raid1 mirrors, where
              each mirror is devices.

       --stripesize Size
              specifies the Size of each stripe in kilobytes.  This is
              the amount of data that is written to one device before
              moving to the next.

       PVs specifies the devices to use.  If not specified, lvm will
       choose the necessary devices.  Devices are used to create mirrors
       in the order listed, e.g. for mirrors 1, stripes 2, listing PV1
       PV2 PV3 PV4 results in mirrors PV1/PV2 and PV3/PV4.

       RAID10 is not mirroring on top of stripes, which would be RAID01,
       which is less tolerant of device failures.

   Configuration Options
       There are a number of options in the LVM configuration file that
       affect the behavior of RAID LVs.  The tunable options are listed
       below.  A detailed description of each can be found in the LVM
       configuration file itself.
              mirror_segtype_default
              raid10_segtype_default
              raid_region_size
              raid_fault_policy
              activation_mode

   Monitoring
       When a RAID LV is activated the dmeventd(8) process is started to
       monitor the health of the LV.  Various events detected in the
       kernel can cause a notification to be sent from device-mapper to
       the monitoring process, including device failures and
       synchronization completion (e.g.  for initialization or
       scrubbing).

       The LVM configuration file contains options that affect how the
       monitoring process will respond to failure events (e.g.
       raid_fault_policy).  It is possible to turn on and off monitoring
       with lvchange, but it is not recommended to turn this off unless
       you have a thorough knowledge of the consequences.

   Synchronization
       Synchronization is the process that makes all the devices in a
       RAID LV consistent with each other.

       In a RAID1 LV, all mirror images should have the same data.  When
       a new mirror image is added, or a mirror image is missing data,
       then images need to be synchronized.  Data blocks are copied from
       an existing image to a new or outdated image to make them match.

       In a RAID 4/5/6 LV, parity blocks and data blocks should match
       based on the parity calculation.  When the devices in a RAID LV
       change, the data and parity blocks can become inconsistent and
       need to be synchronized.  Correct blocks are read, parity is
       calculated, and recalculated blocks are written.

       The RAID implementation keeps track of which parts of a RAID LV
       are synchronized.  When a RAID LV is first created and activated
       the first synchronization is called initialization.  A pointer
       stored in the raid metadata keeps track of the initialization
       process thus allowing it to be restarted after a deactivation of
       the RaidLV or a crash.  Any writes to the RaidLV dirties the
       respective region of the write intent bitmap which allow for fast
       recovery of the regions after a crash.  Without this, the entire
       LV would need to be synchronized every time it was activated.

       Automatic synchronization happens when a RAID LV is activated,
       but it is usually partial because the bitmaps reduce the areas
       that are checked.  A full sync becomes necessary when devices in
       the RAID LV are replaced.

       The synchronization status of a RAID LV is reported by the
       following command, where "Cpy%Sync" = "100%" means sync is
       complete:

       lvs -a -o name,sync_percent

   Scrubbing
       Scrubbing is a full scan of the RAID LV requested by a user.
       Scrubbing can find problems that are missed by partial
       synchronization.

       Scrubbing assumes that RAID metadata and bitmaps may be
       inaccurate, so it verifies all RAID metadata, LV data, and parity
       blocks.  Scrubbing can find inconsistencies caused by hardware
       errors or degradation.  These kinds of problems may be undetected
       by automatic synchronization which excludes areas outside of the
       RAID write-intent bitmap.

       The command to scrub a RAID LV can operate in two different
       modes:

       lvchange --syncaction check|repair LV

       check  Check mode is read-only and only detects inconsistent
              areas in the RAID LV, it does not correct them.

       repair Repair mode checks and writes corrected blocks to
              synchronize any inconsistent areas.

       Scrubbing can consume a lot of bandwidth and slow down
       application I/O on the RAID LV.  To control the I/O rate used for
       scrubbing, use:

       --maxrecoveryrate Size[k|UNIT]
              Sets the maximum recovery rate for a RAID LV.  Size is
              specified as an amount per second for each device in the
              array.  If no suffix is given, then KiB/sec/device is
              used.  Setting the recovery rate to 0 means it will be
              unbounded.

       --minrecoveryrate Size[k|UNIT]
              Sets the minimum recovery rate for a RAID LV.  Size is
              specified as an amount per second for each device in the
              array.  If no suffix is given, then KiB/sec/device is
              used.  Setting the recovery rate to 0 means it will be
              unbounded.

       To display the current scrubbing in progress on an LV, including
       the syncaction mode and percent complete, run:

       lvs -a -o name,raid_sync_action,sync_percent

       After scrubbing is complete, to display the number of
       inconsistent blocks found, run:

       lvs -o name,raid_mismatch_count

       Also, if mismatches were found, the lvs attr field will display
       the letter "m" (mismatch) in the 9th position, e.g.

       # lvs -o name,vgname,segtype,attr vg/lv
         LV VG   Type  Attr
         lv vg   raid1 Rwi-a-r-m-

   Scrubbing Limitations
       The check mode can only report the number of inconsistent blocks,
       it cannot report which blocks are inconsistent.  This makes it
       impossible to know which device has errors, or if the errors
       affect file system data, metadata or nothing at all.

       The repair mode can make the RAID LV data consistent, but it does
       not know which data is correct.  The result may be consistent but
       incorrect data.  When two different blocks of data must be made
       consistent, it chooses the block from the device that would be
       used during RAID initialization.  However, if the PV holding
       corrupt data is known, lvchange --rebuild can be used in place of
       scrubbing to reconstruct the data on the bad device.

       Future developments might include:

       Allowing a user to choose the correct version of data during
       repair.

       Using a majority of devices to determine the correct version of
       data to use in a 3-way RAID1 or RAID6 LV.

       Using a checksumming device to pin-point when and where an error
       occurs, allowing it to be rewritten.

   SubLVs
       An LV is often a combination of other hidden LVs called SubLVs.
       The SubLVs either use physical devices, or are built from other
       SubLVs themselves.  SubLVs hold LV data blocks, RAID parity
       blocks, and RAID metadata.  SubLVs are generally hidden, so the
       lvs -a option is required to display them:

       lvs -a -o name,segtype,devices

       SubLV names begin with the visible LV name, and have an automatic
       suffix indicating its role:

            • SubLVs holding LV data or parity blocks have the suffix
              _rimage_#.
              These SubLVs are sometimes referred to as DataLVs.

            • SubLVs holding RAID metadata have the suffix _rmeta_#.
              RAID metadata includes superblock information, RAID type,
              bitmap, and device health information.
              These SubLVs are sometimes referred to as MetaLVs.

       SubLVs are an internal implementation detail of LVM.  The way
       they are used, constructed and named may change.

       The following examples show the SubLV arrangement for each of the
       basic RAID LV types, using the fewest number of devices allowed
       for each.

       Examples

       raid0
       Each rimage SubLV holds a portion of LV data.  No parity is used.
       No RAID metadata is used.

       # lvcreate --type raid0 --stripes 2 --name lvr0 ...

       # lvs -a -o name,segtype,devices
         lvr0            raid0  lvr0_rimage_0(0),lvr0_rimage_1(0)
         [lvr0_rimage_0] linear /dev/sda(...)
         [lvr0_rimage_1] linear /dev/sdb(...)

       raid1
       Each rimage SubLV holds a complete copy of LV data.  No parity is
       used.  Each rmeta SubLV holds RAID metadata.

       # lvcreate --type raid1 --mirrors 1 --name lvr1 ...

       # lvs -a -o name,segtype,devices
         lvr1            raid1  lvr1_rimage_0(0),lvr1_rimage_1(0)
         [lvr1_rimage_0] linear /dev/sda(...)
         [lvr1_rimage_1] linear /dev/sdb(...)
         [lvr1_rmeta_0]  linear /dev/sda(...)
         [lvr1_rmeta_1]  linear /dev/sdb(...)

       raid4
       At least three rimage SubLVs each hold a portion of LV data and
       one rimage SubLV holds parity.  Each rmeta SubLV holds RAID
       metadata.

       # lvcreate --type raid4 --stripes 2 --name lvr4 ...

       # lvs -a -o name,segtype,devices
         lvr4            raid4  lvr4_rimage_0(0),\
                                lvr4_rimage_1(0),\
                                lvr4_rimage_2(0)
         [lvr4_rimage_0] linear /dev/sda(...)
         [lvr4_rimage_1] linear /dev/sdb(...)
         [lvr4_rimage_2] linear /dev/sdc(...)
         [lvr4_rmeta_0]  linear /dev/sda(...)
         [lvr4_rmeta_1]  linear /dev/sdb(...)
         [lvr4_rmeta_2]  linear /dev/sdc(...)

       raid5
       At least three rimage SubLVs each typically hold a portion of LV
       data and parity (see section on raid5) Each rmeta SubLV holds
       RAID metadata.

       # lvcreate --type raid5 --stripes 2 --name lvr5 ...

       # lvs -a -o name,segtype,devices
         lvr5            raid5  lvr5_rimage_0(0),\
                                lvr5_rimage_1(0),\
                                lvr5_rimage_2(0)
         [lvr5_rimage_0] linear /dev/sda(...)
         [lvr5_rimage_1] linear /dev/sdb(...)
         [lvr5_rimage_2] linear /dev/sdc(...)
         [lvr5_rmeta_0]  linear /dev/sda(...)
         [lvr5_rmeta_1]  linear /dev/sdb(...)
         [lvr5_rmeta_2]  linear /dev/sdc(...)

       raid6
       At least five rimage SubLVs each typically hold a portion of LV
       data and parity.  (see section on raid6) Each rmeta SubLV holds
       RAID metadata.

       # lvcreate --type raid6 --stripes 3 --name lvr6

       # lvs -a -o name,segtype,devices
         lvr6            raid6  lvr6_rimage_0(0),\
                                lvr6_rimage_1(0),\
                                lvr6_rimage_2(0),\
                                lvr6_rimage_3(0),\
                                lvr6_rimage_4(0),\
                                lvr6_rimage_5(0)
         [lvr6_rimage_0] linear /dev/sda(...)
         [lvr6_rimage_1] linear /dev/sdb(...)
         [lvr6_rimage_2] linear /dev/sdc(...)
         [lvr6_rimage_3] linear /dev/sdd(...)
         [lvr6_rimage_4] linear /dev/sde(...)
         [lvr6_rimage_5] linear /dev/sdf(...)
         [lvr6_rmeta_0]  linear /dev/sda(...)
         [lvr6_rmeta_1]  linear /dev/sdb(...)
         [lvr6_rmeta_2]  linear /dev/sdc(...)
         [lvr6_rmeta_3]  linear /dev/sdd(...)
         [lvr6_rmeta_4]  linear /dev/sde(...)
         [lvr6_rmeta_5]  linear /dev/sdf(...)

       raid10
       At least four rimage SubLVs each hold a portion of LV data.  No
       parity is used.  Each rmeta SubLV holds RAID metadata.

       # lvcreate --type raid10 --stripes 2 --mirrors 1 --name lvr10

       # lvs -a -o name,segtype,devices
         lvr10            raid10 lvr10_rimage_0(0),\
                                 lvr10_rimage_1(0),\
                                 lvr10_rimage_2(0),\
                                 lvr10_rimage_3(0)
         [lvr10_rimage_0] linear /dev/sda(...)
         [lvr10_rimage_1] linear /dev/sdb(...)
         [lvr10_rimage_2] linear /dev/sdc(...)
         [lvr10_rimage_3] linear /dev/sdd(...)
         [lvr10_rmeta_0]  linear /dev/sda(...)
         [lvr10_rmeta_1]  linear /dev/sdb(...)
         [lvr10_rmeta_2]  linear /dev/sdc(...)
         [lvr10_rmeta_3]  linear /dev/sdd(...)

DEVICE FAILURE         top

       Physical devices in a RAID LV can fail or be lost for multiple
       reasons.  A device could be disconnected, permanently failed, or
       temporarily disconnected.  The purpose of RAID LVs (levels 1 and
       higher) is to continue operating in a degraded mode, without
       losing LV data, even after a device fails.  The number of devices
       that can fail without the loss of LV data depends on the RAID
       level:
            • RAID0 (striped) LVs cannot tolerate losing any devices.
              LV data will be lost if any devices fail.
            • RAID1 LVs can tolerate losing all but one device without
              LV data loss.
            • RAID4 and RAID5 LVs can tolerate losing one device without
              LV data loss.
            • RAID6 LVs can tolerate losing two devices without LV data
              loss.
            • RAID10 is variable, and depends on which devices are lost.
              It stripes across multiple mirror groups with raid1 layout
              thus it can tolerate losing all but one device in each of
              these groups without LV data loss.

       If a RAID LV is missing devices, or has other device-related
       problems, lvs reports this in the health_status (and attr)
       fields:

       lvs -o name,lv_health_status

       partial
              Devices are missing from the LV.  This is also indicated
              by the letter "p" (partial) in the 9th position of the lvs
              attr field.

       refresh needed
              A device was temporarily missing but has returned.  The LV
              needs to be refreshed to use the device again (which will
              usually require partial synchronization).  This is also
              indicated by the letter "r" (refresh needed) in the 9th
              position of the lvs attr field.  See Refreshing an LV.
              This could also indicate a problem with the device, in
              which case it should be be replaced, see Replacing
              Devices.

       mismatches exist
              See Scrubbing.

       Most commands will also print a warning if a device is missing,
       e.g.
       WARNING: Device for PV uItL3Z-wBME-DQy0-... not found or rejected ...

       This warning will go away if the device returns or is removed
       from the VG (see vgreduce --removemissing).

   Activating an LV with missing devices
       A RAID LV that is missing devices may be activated or not,
       depending on the "activation mode" used in lvchange:

       lvchange -ay --activationmode complete|degraded|partial LV

       complete
              The LV is only activated if all devices are present.

       degraded
              The LV is activated with missing devices if the RAID level
              can tolerate the number of missing devices without LV data
              loss.

       partial
              The LV is always activated, even if portions of the LV
              data are missing because of the missing device(s).  This
              should only be used to perform extreme recovery or repair
              operations.

       Default activation mode when not specified by the command:
       lvm.conf(5) activation/activation_mode

       The default value is printed by:
       # lvmconfig --type default activation/activation_mode

   Replacing Devices
       Devices in a RAID LV can be replaced by other devices in the VG.
       When replacing devices that are no longer visible on the system,
       use lvconvert --repair.  When replacing devices that are still
       visible, use lvconvert --replace.  The repair command will
       attempt to restore the same number of data LVs that were
       previously in the LV.  The replace option can be repeated to
       replace multiple PVs.  Replacement devices can be optionally
       listed with either option.

       lvconvert --repair LV [NewPVs]

       lvconvert --replace OldPV LV [NewPV]

       lvconvert --replace OldPV1 --replace OldPV2 LV [NewPVs]

       New devices require synchronization with existing devices.
       See Synchronization.

   Refreshing an LV
       Refreshing a RAID LV clears any transient device failures (device
       was temporarily disconnected) and returns the LV to its fully
       redundant mode.  Restoring a device will usually require at least
       partial synchronization (see Synchronization).  Failure to clear
       a transient failure results in the RAID LV operating in degraded
       mode until it is reactivated.  Use the lvchange command to
       refresh an LV:

       lvchange --refresh LV

       # lvs -o name,vgname,segtype,attr,size vg
         LV VG   Type  Attr       LSize
         lv vg   raid1 Rwi-a-r-r- 100.00g

       # lvchange --refresh vg/lv

       # lvs -o name,vgname,segtype,attr,size vg
         LV VG   Type  Attr       LSize
         lv vg   raid1 Rwi-a-r--- 100.00g

   Automatic repair
       If a device in a RAID LV fails, device-mapper in the kernel
       notifies the dmeventd(8) monitoring process (see Monitoring).
       dmeventd can be configured to automatically respond using:
       lvm.conf(5) activation/raid_fault_policy

       Possible settings are:

       warn   A warning is added to the system log indicating that a
              device has failed in the RAID LV.  It is left to the user
              to repair the LV, e.g.  replace failed devices.

       allocate
              dmeventd automatically attempts to repair the LV using
              spare devices in the VG.  Note that even a transient
              failure is treated as a permanent failure under this
              setting.  A new device is allocated and full
              synchronization is started.

       The specific command run by dmeventd(8) to warn or repair is:
       lvconvert --repair --use-policies LV

   Corrupted Data
       Data on a device can be corrupted due to hardware errors without
       the device ever being disconnected or there being any fault in
       the software.  This should be rare, and can be detected (see
       Scrubbing).

   Rebuild specific PVs
       If specific PVs in a RAID LV are known to have corrupt data, the
       data on those PVs can be reconstructed with:

       lvchange --rebuild PV LV

       The rebuild option can be repeated with different PVs to replace
       the data on multiple PVs.

DATA INTEGRITY         top

       The device mapper integrity target can be used in combination
       with RAID levels 1,4,5,6,10 to detect and correct data corruption
       in RAID images. A dm-integrity layer is placed above each RAID
       image, and an extra sub LV is created to hold integrity metadata
       (data checksums) for each RAID image.  When data is read from an
       image, integrity checksums are used to detect corruption. If
       detected, dm-raid reads the data from another (good) image to
       return to the caller.  dm-raid will also automatically write the
       good data back to the image with bad data to correct the
       corruption.

       When creating a RAID LV with integrity, or adding integrity,
       space is required for integrity metadata.  Every 500MB of LV data
       requires an additional 4MB to be allocated for integrity
       metadata, for each RAID image.

       Create a RAID LV with integrity:
       lvcreate --type raidN --raidintegrity y

       Add integrity to an existing RAID LV:
       lvconvert --raidintegrity y LV

       Remove integrity from a RAID LV:
       lvconvert --raidintegrity n LV

   Integrity options
       --raidintegritymode journal|bitmap
              Use a journal (default) or bitmap for keeping integrity
              checksums consistent in case of a crash. The bitmap areas
              are recalculated after a crash, so corruption in those
              areas would not be detected. A journal does not have this
              problem.  The journal mode doubles writes to storage, but
              can improve performance for scattered writes packed into a
              single journal write.  bitmap mode can in theory achieve
              full write throughput of the device, but would not benefit
              from the potential scattered write optimization.

       --raidintegrityblocksize 512|1024|2048|4096
              The block size to use for dm-integrity on raid images.
              The integrity block size should usually match the device
              logical block size, or the file system sector/block sizes.
              It may be less than the file system sector/block size, but
              not less than the device logical block size.  Possible
              values: 512, 1024, 2048, 4096.

   Integrity initialization
       When integrity is added to an LV, the kernel needs to initialize
       the integrity metadata (checksums) for all blocks in the LV.  The
       data corruption checking performed by dm-integrity will only
       operate on areas of the LV that are already initialized.  The
       progress of integrity initialization is reported by the
       "syncpercent" LV reporting field (and under the Cpy%Sync lvs
       column.)

   Integrity limitations
       To work around some limitations, it is possible to remove
       integrity from the LV, make the change, then add integrity again.
       (Integrity metadata would need to initialized when added again.)

       LVM must be able to allocate the integrity metadata sub LV on a
       single PV that is already in use by the associated RAID image.
       This can potentially cause a problem during lvextend if the
       original PV holding the image and integrity metadata is full.  To
       work around this limitation, remove integrity, extend the LV, and
       add integrity again.

       Additional RAID images can be added to raid1 LVs, but not to
       other raid levels.

       A raid1 LV with integrity cannot be converted to linear (remove
       integrity to do this.)

       RAID LVs with integrity cannot yet be used as sub LVs with other
       LV types.

       The following are not yet permitted on RAID LVs with integrity:
       lvreduce, pvmove, snapshots, splitmirror, raid syncaction
       commands, raid rebuild.

RAID1 TUNING         top

       A RAID1 LV can be tuned so that certain devices are avoided for
       reading while all devices are still written to.

       lvchange --[raid]writemostly PV[:y|n|t] LV

       The specified device will be marked as "write mostly", which
       means that reading from this device will be avoided, and other
       devices will be preferred for reading (unless no other devices
       are available.)  This minimizes the I/O to the specified device.

       If the PV name has no suffix, the write mostly attribute is set.
       If the PV name has the suffix :n, the write mostly attribute is
       cleared, and the suffix :t toggles the current setting.

       The write mostly option can be repeated on the command line to
       change multiple devices at once.

       To report the current write mostly setting, the lvs attr field
       will show the letter "w" in the 9th position when write mostly is
       set:

       lvs -a -o name,attr

       When a device is marked write mostly, the maximum number of
       outstanding writes to that device can be configured.  Once the
       maximum is reached, further writes become synchronous.  When
       synchronous, a write to the LV will not complete until writes to
       all the mirror images are complete.

       lvchange --[raid]writebehind Number LV

       To report the current write behind setting, run:

       lvs -o name,raid_write_behind

       When write behind is not configured, or set to 0, all LV writes
       are synchronous.

RAID TAKEOVER         top

       RAID takeover is converting a RAID LV from one RAID level to
       another, e.g.  raid5 to raid6.  Changing the RAID level is
       usually done to increase or decrease resilience to device
       failures or to restripe LVs.  This is done using lvconvert and
       specifying the new RAID level as the LV type:

       lvconvert --type RaidLevel LV [PVs]

       The most common and recommended RAID takeover conversions are:

       linear to raid1
              Linear is a single image of LV data, and converting it to
              raid1 adds a mirror image which is a direct copy of the
              original linear image.

       striped/raid0 to raid4/5/6
              Adding parity devices to a striped volume results in
              raid4/5/6.

       Unnatural conversions that are not recommended include converting
       between striped and non-striped types.  This is because file
       systems often optimize I/O patterns based on device striping
       values.  If those values change, it can decrease performance.

       Converting to a higher RAID level requires allocating new SubLVs
       to hold RAID metadata, and new SubLVs to hold parity blocks for
       LV data.  Converting to a lower RAID level removes the SubLVs
       that are no longer needed.

       Conversion often requires full synchronization of the RAID LV
       (see Synchronization).  Converting to RAID1 requires copying all
       LV data blocks to N new images on new devices.  Converting to a
       parity RAID level requires reading all LV data blocks,
       calculating parity, and writing the new parity blocks.
       Synchronization can take a long time depending on the throughpout
       of the devices used and the size of the RaidLV.  It can degrade
       performance. Rate controls also apply to conversion; see
       --minrecoveryrate and --maxrecoveryrate.

       Warning: though it is possible to create striped LVs  with up to
       128 stripes, a maximum of 64 stripes can be converted to raid0,
       63 to raid4/5 and 62 to raid6 because of the added parity SubLVs.
       A striped LV with a maximum of 32 stripes can be converted to
       raid10.

       The following takeover conversions are currently possible:
            • between striped and raid0.
            • between linear and raid1.
            • between mirror and raid1.
            • between raid1 with two images and raid4/5.
            • between striped/raid0 and raid4.
            • between striped/raid0 and raid5.
            • between striped/raid0 and raid6.
            • between raid4 and raid5.
            • between raid4/raid5 and raid6.
            • between striped/raid0 and raid10.
            • between striped and raid4.

   Indirect conversions
       Converting from one raid level to another may require multiple
       steps, converting first to intermediate raid levels.

       linear to raid6

       To convert an LV from linear to raid6:
       1. convert to raid1 with two images
       2. convert to raid5 (internally raid5_ls) with two images
       3. convert to raid5 with three or more stripes (reshape)
       4. convert to raid6 (internally raid6_ls_6)
       5. convert to raid6 (internally raid6_zr, reshape)

       The commands to perform the steps above are:
       1. lvconvert --type raid1 --mirrors 1 LV
       2. lvconvert --type raid5 LV
       3. lvconvert --stripes 3 LV
       4. lvconvert --type raid6 LV
       5. lvconvert --type raid6 LV

       The final conversion from raid6_ls_6 to raid6_zr is done to avoid
       the potential write/recovery performance reduction in raid6_ls_6
       because of the dedicated parity device.  raid6_zr rotates data
       and parity blocks to avoid this.

       linear to striped

       To convert an LV from linear to striped:
       1. convert to raid1 with two images
       2. convert to raid5_n
       3. convert to raid5_n with five 128k stripes (reshape)
       4. convert raid5_n to striped

       The commands to perform the steps above are:
       1. lvconvert --type raid1 --mirrors 1 LV
       2. lvconvert --type raid5_n LV
       3. lvconvert --stripes 5 --stripesize 128k LV
       4. lvconvert --type striped LV

       The raid5_n type in step 2 is used because it has dedicated
       parity SubLVs at the end, and can be converted to striped
       directly.  The stripe size is increased in step 3 to add extra
       space for the conversion process.  This step grows the LV size by
       a factor of five.  After conversion, this extra space can be
       reduced (or used to grow the file system using the LV).

       Reversing these steps will convert a striped LV to linear.

       raid6 to striped

       To convert an LV from raid6_nr to striped:
       1. convert to raid6_n_6
       2. convert to striped

       The commands to perform the steps above are:
       1. lvconvert --type raid6_n_6 LV
       2. lvconvert --type striped LV

       Examples

       Converting an LV from linear to raid1.

       # lvs -a -o name,segtype,size vg
         LV   Type   LSize
         lv   linear 300.00g

       # lvconvert --type raid1 --mirrors 1 vg/lv

       # lvs -a -o name,segtype,size vg
         LV            Type   LSize
         lv            raid1  300.00g
         [lv_rimage_0] linear 300.00g
         [lv_rimage_1] linear 300.00g
         [lv_rmeta_0]  linear   3.00m
         [lv_rmeta_1]  linear   3.00m

       Converting an LV from mirror to raid1.

       # lvs -a -o name,segtype,size vg
         LV            Type   LSize
         lv            mirror 100.00g
         [lv_mimage_0] linear 100.00g
         [lv_mimage_1] linear 100.00g
         [lv_mlog]     linear   3.00m

       # lvconvert --type raid1 vg/lv

       # lvs -a -o name,segtype,size vg
         LV            Type   LSize
         lv            raid1  100.00g
         [lv_rimage_0] linear 100.00g
         [lv_rimage_1] linear 100.00g
         [lv_rmeta_0]  linear   3.00m
         [lv_rmeta_1]  linear   3.00m

       Converting an LV from linear to raid1 (with 3 images).

       # lvconvert --type raid1 --mirrors 2 vg/lv

       Converting an LV from striped (with 4 stripes) to raid6_n_6.

       # lvcreate --stripes 4 -L64M -n lv vg

       # lvconvert --type raid6 vg/lv

       # lvs -a -o lv_name,segtype,sync_percent,data_copies
         LV            Type      Cpy%Sync #Cpy
         lv            raid6_n_6 100.00      3
         [lv_rimage_0] linear
         [lv_rimage_1] linear
         [lv_rimage_2] linear
         [lv_rimage_3] linear
         [lv_rimage_4] linear
         [lv_rimage_5] linear
         [lv_rmeta_0]  linear
         [lv_rmeta_1]  linear
         [lv_rmeta_2]  linear
         [lv_rmeta_3]  linear
         [lv_rmeta_4]  linear
         [lv_rmeta_5]  linear

       This convert begins by allocating MetaLVs (rmeta_#) for each of
       the existing stripe devices.  It then creates 2 additional
       MetaLV/DataLV pairs (rmeta_#/rimage_#) for dedicated raid6
       parity.

       If rotating data/parity is required, such as with raid6_nr, it
       must be done by reshaping (see below).

RAID RESHAPING         top

       RAID reshaping is changing attributes of a RAID LV while keeping
       the same RAID level.  This includes changing RAID layout, stripe
       size, or number of stripes.

       When changing the RAID layout or stripe size, no new SubLVs
       (MetaLVs or DataLVs) need to be allocated, but DataLVs are
       extended by a small amount (typically 1 extent).  The extra space
       allows blocks in a stripe to be updated safely, and not be
       corrupted in case of a crash.  If a crash occurs, reshaping can
       just be restarted.

       (If blocks in a stripe were updated in place, a crash could leave
       them partially updated and corrupted.  Instead, an existing
       stripe is quiesced, read, changed in layout, and the new stripe
       written to free space.  Once that is done, the new stripe is
       unquiesced and used.)

       Examples
       (Command output shown in examples may change.)

       Converting raid6_n_6 to raid6_nr with rotating data/parity.

       This conversion naturally follows a previous conversion from
       striped/raid0 to raid6_n_6 (shown above).  It completes the
       transition to a more traditional RAID6.

       # lvs -o lv_name,segtype,sync_percent,data_copies
         LV            Type      Cpy%Sync #Cpy
         lv            raid6_n_6 100.00      3
         [lv_rimage_0] linear
         [lv_rimage_1] linear
         [lv_rimage_2] linear
         [lv_rimage_3] linear
         [lv_rimage_4] linear
         [lv_rimage_5] linear
         [lv_rmeta_0]  linear
         [lv_rmeta_1]  linear
         [lv_rmeta_2]  linear
         [lv_rmeta_3]  linear
         [lv_rmeta_4]  linear
         [lv_rmeta_5]  linear

       # lvconvert --type raid6_nr vg/lv

       # lvs -a -o lv_name,segtype,sync_percent,data_copies
         LV            Type     Cpy%Sync #Cpy
         lv            raid6_nr 100.00      3
         [lv_rimage_0] linear
         [lv_rimage_0] linear
         [lv_rimage_1] linear
         [lv_rimage_1] linear
         [lv_rimage_2] linear
         [lv_rimage_2] linear
         [lv_rimage_3] linear
         [lv_rimage_3] linear
         [lv_rimage_4] linear
         [lv_rimage_5] linear
         [lv_rmeta_0]  linear
         [lv_rmeta_1]  linear
         [lv_rmeta_2]  linear
         [lv_rmeta_3]  linear
         [lv_rmeta_4]  linear
         [lv_rmeta_5]  linear

       The DataLVs are larger (additional segment in each) which
       provides space for out-of-place reshaping.  The result is:

       # lvs -a -o lv_name,segtype,seg_pe_ranges,dataoffset
         LV            Type     PE Ranges          DOff
         lv            raid6_nr lv_rimage_0:0-32 \
                                lv_rimage_1:0-32 \
                                lv_rimage_2:0-32 \
                                lv_rimage_3:0-32
         [lv_rimage_0] linear   /dev/sda:0-31      2048
         [lv_rimage_0] linear   /dev/sda:33-33
         [lv_rimage_1] linear   /dev/sdaa:0-31     2048
         [lv_rimage_1] linear   /dev/sdaa:33-33
         [lv_rimage_2] linear   /dev/sdab:1-33     2048
         [lv_rimage_3] linear   /dev/sdac:1-33     2048
         [lv_rmeta_0]  linear   /dev/sda:32-32
         [lv_rmeta_1]  linear   /dev/sdaa:32-32
         [lv_rmeta_2]  linear   /dev/sdab:0-0
         [lv_rmeta_3]  linear   /dev/sdac:0-0

       All segments with PE ranges '33-33' provide the out-of-place
       reshape space.  The dataoffset column shows that the data was
       moved from initial offset 0 to 2048 sectors on each component
       DataLV.

       For performance reasons the raid6_nr RaidLV can be restriped.
       Convert it from 3-way striped to 5-way-striped.

       # lvconvert --stripes 5 vg/lv
         Using default stripesize 64.00 KiB.
         WARNING: Adding stripes to active logical volume vg/lv will \
         grow it from 99 to 165 extents!
         Run "lvresize -l99 vg/lv" to shrink it or use the additional \
         capacity.
         Logical volume vg/lv successfully converted.

       # lvs vg/lv
         LV   VG     Attr       LSize   Cpy%Sync
         lv   vg     rwi-a-r-s- 652.00m 52.94

       # lvs -a -o lv_name,attr,segtype,seg_pe_ranges,dataoffset vg
         LV            Attr       Type     PE Ranges          DOff
         lv            rwi-a-r--- raid6_nr lv_rimage_0:0-33 \
                                           lv_rimage_1:0-33 \
                                           lv_rimage_2:0-33 ... \
                                           lv_rimage_5:0-33 \
                                           lv_rimage_6:0-33   0
         [lv_rimage_0] iwi-aor--- linear   /dev/sda:0-32      0
         [lv_rimage_0] iwi-aor--- linear   /dev/sda:34-34
         [lv_rimage_1] iwi-aor--- linear   /dev/sdaa:0-32     0
         [lv_rimage_1] iwi-aor--- linear   /dev/sdaa:34-34
         [lv_rimage_2] iwi-aor--- linear   /dev/sdab:0-32     0
         [lv_rimage_2] iwi-aor--- linear   /dev/sdab:34-34
         [lv_rimage_3] iwi-aor--- linear   /dev/sdac:1-34     0
         [lv_rimage_4] iwi-aor--- linear   /dev/sdad:1-34     0
         [lv_rimage_5] iwi-aor--- linear   /dev/sdae:1-34     0
         [lv_rimage_6] iwi-aor--- linear   /dev/sdaf:1-34     0
         [lv_rmeta_0]  ewi-aor--- linear   /dev/sda:33-33
         [lv_rmeta_1]  ewi-aor--- linear   /dev/sdaa:33-33
         [lv_rmeta_2]  ewi-aor--- linear   /dev/sdab:33-33
         [lv_rmeta_3]  ewi-aor--- linear   /dev/sdac:0-0
         [lv_rmeta_4]  ewi-aor--- linear   /dev/sdad:0-0
         [lv_rmeta_5]  ewi-aor--- linear   /dev/sdae:0-0
         [lv_rmeta_6]  ewi-aor--- linear   /dev/sdaf:0-0

       Stripes also can be removed from raid5 and 6.  Convert the 5-way
       striped raid6_nr LV to 4-way-striped.  The force option needs to
       be used, because removing stripes (i.e. image SubLVs) from a
       RaidLV will shrink its size.

       # lvconvert --stripes 4 vg/lv
         Using default stripesize 64.00 KiB.
         WARNING: Removing stripes from active logical volume vg/lv will \
         shrink it from 660.00 MiB to 528.00 MiB!
         THIS MAY DESTROY (PARTS OF) YOUR DATA!
         If that leaves the logical volume larger than 206 extents due \
         to stripe rounding,
         you may want to grow the content afterwards (filesystem etc.)
         WARNING: to remove freed stripes after the conversion has finished,\
         you have to run "lvconvert --stripes 4 vg/lv"
         Logical volume vg/lv successfully converted.

       # lvs -a -o lv_name,attr,segtype,seg_pe_ranges,dataoffset vg
         LV            Attr       Type     PE Ranges          DOff
         lv            rwi-a-r-s- raid6_nr lv_rimage_0:0-33 \
                                           lv_rimage_1:0-33 \
                                           lv_rimage_2:0-33 ... \
                                           lv_rimage_5:0-33 \
                                           lv_rimage_6:0-33   0
         [lv_rimage_0] Iwi-aor--- linear   /dev/sda:0-32      0
         [lv_rimage_0] Iwi-aor--- linear   /dev/sda:34-34
         [lv_rimage_1] Iwi-aor--- linear   /dev/sdaa:0-32     0
         [lv_rimage_1] Iwi-aor--- linear   /dev/sdaa:34-34
         [lv_rimage_2] Iwi-aor--- linear   /dev/sdab:0-32     0
         [lv_rimage_2] Iwi-aor--- linear   /dev/sdab:34-34
         [lv_rimage_3] Iwi-aor--- linear   /dev/sdac:1-34     0
         [lv_rimage_4] Iwi-aor--- linear   /dev/sdad:1-34     0
         [lv_rimage_5] Iwi-aor--- linear   /dev/sdae:1-34     0
         [lv_rimage_6] Iwi-aor-R- linear   /dev/sdaf:1-34     0
         [lv_rmeta_0]  ewi-aor--- linear   /dev/sda:33-33
         [lv_rmeta_1]  ewi-aor--- linear   /dev/sdaa:33-33
         [lv_rmeta_2]  ewi-aor--- linear   /dev/sdab:33-33
         [lv_rmeta_3]  ewi-aor--- linear   /dev/sdac:0-0
         [lv_rmeta_4]  ewi-aor--- linear   /dev/sdad:0-0
         [lv_rmeta_5]  ewi-aor--- linear   /dev/sdae:0-0
         [lv_rmeta_6]  ewi-aor-R- linear   /dev/sdaf:0-0

       The 's' in column 9 of the attribute field shows the RaidLV is
       still reshaping.  The 'R' in the same column of the attribute
       field shows the freed image Sub LVs which will need removing once
       the reshaping finished.

       # lvs -o lv_name,attr,segtype,seg_pe_ranges,dataoffset vg
         LV   Attr       Type     PE Ranges          DOff
         lv   rwi-a-r-R- raid6_nr lv_rimage_0:0-33 \
                                  lv_rimage_1:0-33 \
                                  lv_rimage_2:0-33 ... \
                                  lv_rimage_5:0-33 \
                                  lv_rimage_6:0-33   8192

       Now that the reshape is finished the 'R' attribute on the RaidLV
       shows images can be removed.

       # lvs -o lv_name,attr,segtype,seg_pe_ranges,dataoffset vg
         LV   Attr       Type     PE Ranges          DOff
         lv   rwi-a-r-R- raid6_nr lv_rimage_0:0-33 \
                                  lv_rimage_1:0-33 \
                                  lv_rimage_2:0-33 ... \
                                  lv_rimage_5:0-33 \
                                  lv_rimage_6:0-33   8192

       This is achieved by repeating the command ("lvconvert --stripes 4
       vg/lv" would be sufficient).

       # lvconvert --stripes 4 vg/lv
         Using default stripesize 64.00 KiB.
         Logical volume vg/lv successfully converted.

       # lvs -a -o lv_name,attr,segtype,seg_pe_ranges,dataoffset vg
         LV            Attr       Type     PE Ranges          DOff
         lv            rwi-a-r--- raid6_nr lv_rimage_0:0-33 \
                                           lv_rimage_1:0-33 \
                                           lv_rimage_2:0-33 ... \
                                           lv_rimage_5:0-33   8192
         [lv_rimage_0] iwi-aor--- linear   /dev/sda:0-32      8192
         [lv_rimage_0] iwi-aor--- linear   /dev/sda:34-34
         [lv_rimage_1] iwi-aor--- linear   /dev/sdaa:0-32     8192
         [lv_rimage_1] iwi-aor--- linear   /dev/sdaa:34-34
         [lv_rimage_2] iwi-aor--- linear   /dev/sdab:0-32     8192
         [lv_rimage_2] iwi-aor--- linear   /dev/sdab:34-34
         [lv_rimage_3] iwi-aor--- linear   /dev/sdac:1-34     8192
         [lv_rimage_4] iwi-aor--- linear   /dev/sdad:1-34     8192
         [lv_rimage_5] iwi-aor--- linear   /dev/sdae:1-34     8192
         [lv_rmeta_0]  ewi-aor--- linear   /dev/sda:33-33
         [lv_rmeta_1]  ewi-aor--- linear   /dev/sdaa:33-33
         [lv_rmeta_2]  ewi-aor--- linear   /dev/sdab:33-33
         [lv_rmeta_3]  ewi-aor--- linear   /dev/sdac:0-0
         [lv_rmeta_4]  ewi-aor--- linear   /dev/sdad:0-0
         [lv_rmeta_5]  ewi-aor--- linear   /dev/sdae:0-0

       # lvs -a -o lv_name,attr,segtype,reshapelen vg
         LV            Attr       Type     RSize
         lv            rwi-a-r--- raid6_nr 24.00m
         [lv_rimage_0] iwi-aor--- linear    4.00m
         [lv_rimage_0] iwi-aor--- linear
         [lv_rimage_1] iwi-aor--- linear    4.00m
         [lv_rimage_1] iwi-aor--- linear
         [lv_rimage_2] iwi-aor--- linear    4.00m
         [lv_rimage_2] iwi-aor--- linear
         [lv_rimage_3] iwi-aor--- linear    4.00m
         [lv_rimage_4] iwi-aor--- linear    4.00m
         [lv_rimage_5] iwi-aor--- linear    4.00m
         [lv_rmeta_0]  ewi-aor--- linear
         [lv_rmeta_1]  ewi-aor--- linear
         [lv_rmeta_2]  ewi-aor--- linear
         [lv_rmeta_3]  ewi-aor--- linear
         [lv_rmeta_4]  ewi-aor--- linear
         [lv_rmeta_5]  ewi-aor--- linear

       Future developments might include automatic removal of the freed
       images.

       If the reshape space shall be removed any lvconvert command not
       changing the layout can be used:

       # lvconvert --stripes 4 vg/lv
         Using default stripesize 64.00 KiB.
         No change in RAID LV vg/lv layout, freeing reshape space.
         Logical volume vg/lv successfully converted.

       # lvs -a -o lv_name,attr,segtype,reshapelen vg
         LV            Attr       Type     RSize
         lv            rwi-a-r--- raid6_nr    0
         [lv_rimage_0] iwi-aor--- linear      0
         [lv_rimage_0] iwi-aor--- linear
         [lv_rimage_1] iwi-aor--- linear      0
         [lv_rimage_1] iwi-aor--- linear
         [lv_rimage_2] iwi-aor--- linear      0
         [lv_rimage_2] iwi-aor--- linear
         [lv_rimage_3] iwi-aor--- linear      0
         [lv_rimage_4] iwi-aor--- linear      0
         [lv_rimage_5] iwi-aor--- linear      0
         [lv_rmeta_0]  ewi-aor--- linear
         [lv_rmeta_1]  ewi-aor--- linear
         [lv_rmeta_2]  ewi-aor--- linear
         [lv_rmeta_3]  ewi-aor--- linear
         [lv_rmeta_4]  ewi-aor--- linear
         [lv_rmeta_5]  ewi-aor--- linear

       In case the RaidLV should be converted to striped:

       # lvconvert --type striped vg/lv
         Unable to convert LV vg/lv from raid6_nr to striped.
         Converting vg/lv from raid6_nr is directly possible to the \
         following layouts:
           raid6_nc
           raid6_zr
           raid6_la_6
           raid6_ls_6
           raid6_ra_6
           raid6_rs_6
           raid6_n_6

       A direct conversion isn't possible thus the command informed
       about the possible ones.  raid6_n_6 is suitable to convert to
       striped so convert to it first (this is a reshape changing the
       raid6 layout from raid6_nr to raid6_n_6).

       # lvconvert --type raid6_n_6
         Using default stripesize 64.00 KiB.
         Converting raid6_nr LV vg/lv to raid6_n_6.
       Are you sure you want to convert raid6_nr LV vg/lv? [y/n]: y
         Logical volume vg/lv successfully converted.

       Wait for the reshape to finish.

       # lvconvert --type striped vg/lv
         Logical volume vg/lv successfully converted.

       # lvs -o lv_name,attr,segtype,seg_pe_ranges,dataoffset vg
         LV   Attr       Type    PE Ranges  DOff
         lv   -wi-a----- striped /dev/sda:2-32 \
                                 /dev/sdaa:2-32 \
                                 /dev/sdab:2-32 \
                                 /dev/sdac:3-33
         lv   -wi-a----- striped /dev/sda:34-35 \
                                 /dev/sdaa:34-35 \
                                 /dev/sdab:34-35 \
                                 /dev/sdac:34-35

       From striped we can convert to raid10

       # lvconvert --type raid10 vg/lv
         Using default stripesize 64.00 KiB.
         Logical volume vg/lv successfully converted.

       # lvs -o lv_name,attr,segtype,seg_pe_ranges,dataoffset vg
         LV   Attr       Type   PE Ranges          DOff
         lv   rwi-a-r--- raid10 lv_rimage_0:0-32 \
                                lv_rimage_4:0-32 \
                                lv_rimage_1:0-32 ... \
                                lv_rimage_3:0-32 \
                                lv_rimage_7:0-32   0

       # lvs -a -o lv_name,attr,segtype,seg_pe_ranges,dataoffset vg
         WARNING: Cannot find matching striped segment for vg/lv_rimage_3.
         LV            Attr       Type   PE Ranges          DOff
         lv            rwi-a-r--- raid10 lv_rimage_0:0-32 \
                                         lv_rimage_4:0-32 \
                                         lv_rimage_1:0-32 ... \
                                         lv_rimage_3:0-32 \
                                         lv_rimage_7:0-32   0
         [lv_rimage_0] iwi-aor--- linear /dev/sda:2-32      0
         [lv_rimage_0] iwi-aor--- linear /dev/sda:34-35
         [lv_rimage_1] iwi-aor--- linear /dev/sdaa:2-32     0
         [lv_rimage_1] iwi-aor--- linear /dev/sdaa:34-35
         [lv_rimage_2] iwi-aor--- linear /dev/sdab:2-32     0
         [lv_rimage_2] iwi-aor--- linear /dev/sdab:34-35
         [lv_rimage_3] iwi-XXr--- linear /dev/sdac:3-35     0
         [lv_rimage_4] iwi-aor--- linear /dev/sdad:1-33     0
         [lv_rimage_5] iwi-aor--- linear /dev/sdae:1-33     0
         [lv_rimage_6] iwi-aor--- linear /dev/sdaf:1-33     0
         [lv_rimage_7] iwi-aor--- linear /dev/sdag:1-33     0
         [lv_rmeta_0]  ewi-aor--- linear /dev/sda:0-0
         [lv_rmeta_1]  ewi-aor--- linear /dev/sdaa:0-0
         [lv_rmeta_2]  ewi-aor--- linear /dev/sdab:0-0
         [lv_rmeta_3]  ewi-aor--- linear /dev/sdac:0-0
         [lv_rmeta_4]  ewi-aor--- linear /dev/sdad:0-0
         [lv_rmeta_5]  ewi-aor--- linear /dev/sdae:0-0
         [lv_rmeta_6]  ewi-aor--- linear /dev/sdaf:0-0
         [lv_rmeta_7]  ewi-aor--- linear /dev/sdag:0-0

       raid10 allows to add stripes but can't remove them.

       A more elaborate example to convert from linear to striped with
       interim conversions to raid1 then raid5 followed by restripe (4
       steps).

       We start with the linear LV.

       # lvs -a -o name,size,segtype,syncpercent,datastripes,\
                   stripesize,reshapelenle,devices vg
         LV   LSize   Type   Cpy%Sync #DStr Stripe RSize Devices
         lv   128.00m linear              1     0        /dev/sda(0)

       Then convert it to a 2-way raid1.

       # lvconvert --mirrors 1 vg/lv
         Logical volume vg/lv successfully converted.

       # lvs -a -o name,size,segtype,datastripes,\
                   stripesize,reshapelenle,devices vg
         LV            LSize   Type   #DStr Stripe RSize Devices
         lv            128.00m raid1      2     0        lv_rimage_0(0),\
                                                         lv_rimage_1(0)
         [lv_rimage_0] 128.00m linear     1     0        /dev/sda(0)
         [lv_rimage_1] 128.00m linear     1     0        /dev/sdhx(1)
         [lv_rmeta_0]    4.00m linear     1     0        /dev/sda(32)
         [lv_rmeta_1]    4.00m linear     1     0        /dev/sdhx(0)

       Once the raid1 LV is fully synchronized we convert it to raid5_n
       (only 2-way raid1 LVs can be converted to raid5).  We select
       raid5_n here because it has dedicated parity SubLVs at the end
       and can be converted to striped directly without any additional
       conversion.

       # lvconvert --type raid5_n vg/lv
         Using default stripesize 64.00 KiB.
         Logical volume vg/lv successfully converted.

       # lvs -a -o name,size,segtype,syncpercent,datastripes,\
                   stripesize,reshapelenle,devices vg
         LV            LSize   Type    #DStr Stripe RSize Devices
         lv            128.00m raid5_n     1 64.00k     0 lv_rimage_0(0),\
                                                          lv_rimage_1(0)
         [lv_rimage_0] 128.00m linear      1     0      0 /dev/sda(0)
         [lv_rimage_1] 128.00m linear      1     0      0 /dev/sdhx(1)
         [lv_rmeta_0]    4.00m linear      1     0        /dev/sda(32)
         [lv_rmeta_1]    4.00m linear      1     0        /dev/sdhx(0)

       Now we'll change the number of data stripes from 1 to 5 and
       request 128K stripe size in one command.  This will grow the size
       of the LV by a factor of 5 (we add 4 data stripes to the one
       given).  That additional space can be used by e.g. growing any
       contained filesystem or the LV can be reduced in size after the
       reshaping conversion has finished.

       # lvconvert --stripesize 128k --stripes 5 vg/lv
         Converting stripesize 64.00 KiB of raid5_n LV vg/lv to 128.00 KiB.
         WARNING: Adding stripes to active logical volume vg/lv will grow \
         it from 32 to 160 extents!
         Run "lvresize -l32 vg/lv" to shrink it or use the additional capacity.
         Logical volume vg/lv successfully converted.

       # lvs -a -o name,size,segtype,datastripes,\
                   stripesize,reshapelenle,devices
         LV            LSize   Type    #DStr Stripe  RSize Devices
         lv            640.00m raid5_n     5 128.00k     6 lv_rimage_0(0),\
                                                           lv_rimage_1(0),\
                                                           lv_rimage_2(0),\
                                                           lv_rimage_3(0),\
                                                           lv_rimage_4(0),\
                                                           lv_rimage_5(0)
         [lv_rimage_0] 132.00m linear      1      0      1 /dev/sda(33)
         [lv_rimage_0] 132.00m linear      1      0        /dev/sda(0)
         [lv_rimage_1] 132.00m linear      1      0      1 /dev/sdhx(33)
         [lv_rimage_1] 132.00m linear      1      0        /dev/sdhx(1)
         [lv_rimage_2] 132.00m linear      1      0      1 /dev/sdhw(33)
         [lv_rimage_2] 132.00m linear      1      0        /dev/sdhw(1)
         [lv_rimage_3] 132.00m linear      1      0      1 /dev/sdhv(33)
         [lv_rimage_3] 132.00m linear      1      0        /dev/sdhv(1)
         [lv_rimage_4] 132.00m linear      1      0      1 /dev/sdhu(33)
         [lv_rimage_4] 132.00m linear      1      0        /dev/sdhu(1)
         [lv_rimage_5] 132.00m linear      1      0      1 /dev/sdht(33)
         [lv_rimage_5] 132.00m linear      1      0        /dev/sdht(1)
         [lv_rmeta_0]    4.00m linear      1      0        /dev/sda(32)
         [lv_rmeta_1]    4.00m linear      1      0        /dev/sdhx(0)
         [lv_rmeta_2]    4.00m linear      1      0        /dev/sdhw(0)
         [lv_rmeta_3]    4.00m linear      1      0        /dev/sdhv(0)
         [lv_rmeta_4]    4.00m linear      1      0        /dev/sdhu(0)
         [lv_rmeta_5]    4.00m linear      1      0        /dev/sdht(0)

       Once the conversion has finished we can can convert to striped.

       # lvconvert --type striped vg/lv
         Logical volume vg/lv successfully converted.

       # lvs -a -o name,size,segtype,datastripes,\
                   stripesize,reshapelenle,devices vg
         LV   LSize   Type    #DStr Stripe  RSize Devices
         lv   640.00m striped     5 128.00k       /dev/sda(33),\
                                                  /dev/sdhx(33),\
                                                  /dev/sdhw(33),\
                                                  /dev/sdhv(33),\
                                                  /dev/sdhu(33)
         lv   640.00m striped     5 128.00k       /dev/sda(0),\
                                                  /dev/sdhx(1),\
                                                  /dev/sdhw(1),\
                                                  /dev/sdhv(1),\
                                                  /dev/sdhu(1)

       Reversing these steps will convert a given striped LV to linear.

       Mind the facts that stripes are removed thus the capacity of the
       RaidLV will shrink and that changing the RaidLV layout will
       influence its performance.

       "lvconvert --stripes 1 vg/lv" for converting to 1 stripe will
       inform upfront about the reduced size to allow for resizing the
       content or growing the RaidLV before actually converting to 1
       stripe.  The --force option is needed to allow stripe removing
       conversions to prevent data loss.

       Of course any interim step can be the intended last one (e.g.
       striped → raid1).

RAID5 VARIANTS         top

       raid5_ls
            • RAID5 left symmetric
            • Rotating parity N with data restart

       raid5_la
            • RAID5 left asymmetric
            • Rotating parity N with data continuation

       raid5_rs
            • RAID5 right symmetric
            • Rotating parity 0 with data restart

       raid5_ra
            • RAID5 right asymmetric
            • Rotating parity 0 with data continuation

       raid5_n
            • RAID5 parity n
            • Dedicated parity device n used for striped/raid0
              conversions
            • Used for RAID Takeover

RAID6 VARIANTS         top

       raid6
            • RAID6 zero restart (aka left symmetric)
            • Rotating parity 0 with data restart
            • Same as raid6_zr

       raid6_zr
            • RAID6 zero restart (aka left symmetric)
            • Rotating parity 0 with data restart

       raid6_nr
            • RAID6 N restart (aka right symmetric)
            • Rotating parity N with data restart

       raid6_nc
            • RAID6 N continue
            • Rotating parity N with data continuation

       raid6_n_6
            • RAID6 last parity devices
            • Fixed dedicated last devices (P-Syndrome N-1 and Q-
              Syndrome N) with striped data used for striped/raid0
              conversions
            • Used for RAID Takeover

       raid6_{ls,rs,la,ra}_6
            • RAID6 last parity device
            • Dedicated last parity device used for conversions from/to
              raid5_{ls,rs,la,ra}

       raid6_ls_6
            • RAID6 N continue
            • Same as raid5_ls for N-1 devices with fixed Q-Syndrome N
            • Used for RAID Takeover

       raid6_la_6
            • RAID6 N continue
            • Same as raid5_la for N-1 devices with fixed Q-Syndrome N
            • Used forRAID Takeover

       raid6_rs_6
            • RAID6 N continue
            • Same as raid5_rs for N-1 devices with fixed Q-Syndrome N
            • Used for RAID Takeover

       raid6_ra_6
            • RAID6 N continue
            • Same as raid5_ra for N-1 devices with fixed Q-Syndrome N
            • Used for RAID Takeover

HISTORY         top

       The 2.6.38-rc1 version of the Linux kernel introduced a device-
       mapper target to interface with the software RAID (MD)
       personalities.  This provided device-mapper with RAID 4/5/6
       capabilities and a larger development community.  Later, support
       for RAID1, RAID10, and RAID1E (RAID 10 variants) were added.
       Support for these new kernel RAID targets was added to LVM
       version 2.02.87.  The capabilities of the LVM raid1 type have
       surpassed the old mirror type.  raid1 is now recommended instead
       of mirror.  raid1 became the default for mirroring in LVM version
       2.02.100.

SEE ALSO         top

       lvm(8), lvm.conf(5), lvcreate(8), lvconvert(8), lvchange(8),
       lvextend(8), dmeventd(8)

COLOPHON         top

       This page is part of the lvm2 (Logical Volume Manager 2) project.
       Information about the project can be found at 
       ⟨http://www.sourceware.org/lvm2/⟩.  If you have a bug report for
       this manual page, see ⟨https://github.com/lvmteam/lvm2/issues⟩.
       This page was obtained from the tarball
       https://github.com/lvmteam/lvm2/archive/refs/tags/v2_03_13.tar.gz
       fetched from ⟨https://github.com/lvmteam/lvm2/releases⟩ on
       2021-08-27.  If you discover any rendering problems in this HTML
       version of the page, or you believe there is a better or more up-
       to-date source for the page, or you have corrections or
       improvements to the information in this COLOPHON (which is not
       part of the original manual page), send a mail to
       man-pages@man7.org

Red Hat, Inc        LVM TOOLS 2.03.13(2) (2021-08-11)         LVMRAID(7)

Pages that refer to this page: lvchange(8)lvconvert(8)lvcreate(8)lvdisplay(8)lvextend(8)lvm(8)lvmconfig(8)lvmdevices(8)lvmdiskscan(8)lvm-fullreport(8)lvm-lvpoll(8)lvreduce(8)lvremove(8)lvrename(8)lvresize(8)lvs(8)lvscan(8)pvchange(8)pvck(8)pvcreate(8)pvdisplay(8)pvmove(8)pvremove(8)pvresize(8)pvs(8)pvscan(8)vgcfgbackup(8)vgcfgrestore(8)vgchange(8)vgck(8)vgconvert(8)vgcreate(8)vgdisplay(8)vgexport(8)vgextend(8)vgimport(8)vgimportclone(8)vgimportdevices(8)vgmerge(8)vgmknodes(8)vgreduce(8)vgremove(8)vgrename(8)vgs(8)vgscan(8)vgsplit(8)