BTREPLAY(8)                                                      BTREPLAY(8)

NAME         top

       btreplay - recreate IO loads recorded by blktrace

SYNOPSIS         top

       btreplay [ options ] <dev...>

DESCRIPTION         top

       The btrecord and btreplay tools provide the ability to record and
       replay IOs captured by the blktrace utility. Attempts are made to
       maintain ordering, CPU mappings and time-separation of IOs.

       The blktrace utility provides the ability to collect detailed traces
       from the kernel for each IO processed by the block IO layer. The
       traces provide a complete timeline for each IO processed, including
       detailed information concerning when an IO was first received by the
       block IO layer — indicating the device, CPU number, time stamp, IO
       direction, sector number and IO size (number of sectors). Using this
       information, one is able to replay the IO again on the same machine
       or another set up entirely.

       The basic operating work-flow to replay IOs would be something like:

           Run blktrace to collect traces. Here you specify the
           device or devices that you wish to trace and later replay IOs
         upon. Note:
           the only traces you are interested in are QUEUE requests —
           thus, to save system resources (including storage for traces),
         one could
           specify the -a queue command line option to blktrace.

           While blktrace is running, you run the workload that you
           are interested in.

           When the work load has completed, you stop the blktrace
           utility (thus saving all traces over the complete workload).

           You extract the pertinent IO information from the traces saved by
           blktrace using the btrecord utility. This will parse
           each trace file created by blktrace, and crafty IO descriptions
           to be used in the next phase of the workload processing.

           Once btrecord has successfully created a series of data
           files to be processed, you can run the btreplay utility which
           attempts to generate the same IOs seen during the sample workload

OPTIONS         top

       -c <num>
              Set number of CPUs to use.

       -d <dir>
              Set input directory.  This option requires a single parameter
              providing the directory name for where input files are to be
              found. The default directory is the current directory (.).

              Find record files automatically This option instructs btreplay
              to go find all the record files in the directory specified
              (either via the -d option, or in the default directory (.).

              Show help and exit.

       -i <basename>
              Set base name for input files.  Each input file has 3 fields:

                  Device identifier (taken directly from the device name of
                  blktrace output file).

                  btrecord base name — by default ``replay''.

                  The CPU number (again, taken directly from the
                  blktrace output file name).

              This option requires a single parameter that will override the
              default name (replay), and replace it with the specified

       -I <num>
              Set number of iterations to run.  This option requires a
              single parameter which specifies the number of times to run
              through the input files. The default value is 1

       -M <filename>
              Specify device mappings.  This option requires a single
              parameter which specifies the name of a file contain device
              mappings. The file must be very simply managed, with just two
              pieces of data per line:

                  The device name on the recorded system (with the '/dev/'
                  removed). Example: /dev/sda would just be sda.

                  The device name on the replay system to use (again,
                without the
                  '/dev/' path prepended).

              An example file for when one would map devices /dev/sda and
              /dev/sdb on the recorded system to dev/sdg and sdh on the
              replay system would be:

                     sda sdg
                     sdb sdh

              The only entries in the file that are allowed are these two
              element lines — we do not (yet?) support the notion of blank
              lines, or comment lines, or the like.

              The utility allows for multiple -M options to be supplied on
              the command line.

              Disable pre-bunch stalls.  When specified on the command line,
              all pre-bunch stall indicators will be ignored. IOs will be
              replayed without inter-bunch delays.

       -x <factor>
              Specify acceleration factor. Default value is 1 (no

              Enable verbose output.  When specified on the command line,
              this option instructs btreplay to store information concerning
              each stall and IO operation performed by btreplay. The name of
              each file so created will be the input file name used with an
              extension of .rep appended onto it. Thus, an input file of the
              name sdab.replay.3 would generate a verbose output file with
              the name sdab.replay.3.rep in the directory specified for
              input files.

              In addition, btreplay will also output to stderr the names of
              the input files being processed.

              Show version number and exit.

              Enable writing during replay.  As a precautionary measure, by
              default btreplay will not process write requests. In order to
              enable btreplay to actually write to devices one must
              explicitly specify the -W option.

AUTHORS         top

       btreplay was written by Alan D. Brunelle.  This man page was created
       from the btreplay documentation by Bas Zoetekouw.

REPORTING BUGS         top

       Report bugs to <>

COPYRIGHT         top

       Copyright © 2007 Alan D. Brunelle, Alan D. Brunelle and Nathan Scott.
       This is free software.  You may redistribute copies of it under the
       terms of the GNU General Public License
       <>.  There is NO WARRANTY, to the
       extent permitted by law.
       This manual page was created for Debian by Bas Zoetekouw.  It was
       derived from the documentation provided by the authors and it may be
       used, distributed and modified under the terms of the GNU General
       Public License, version 2.
       On Debian systems, the text of the GNU General Public License can be
       found in /usr/share/common-licenses/GPL-2.

SEE ALSO         top

       The full documentation for btreplay can be found in
       /usr/share/doc/blktrace on Debian systems.
       blktrace (8), blkparse (1), btrecord (8)

COLOPHON         top

       This page is part of the blktrace (Linux block layer I/O tracer)
       project.  Information about the project can be found at [unknown --
       if you know, please contact] It is not known how
       to report bugs for this man page; if you know, please send a mail to  This page was obtained from the project's
       upstream Git repository 
       ⟨⟩ on
       2017-03-13.  If you discover any rendering problems in this HTML ver‐
       sion 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 man‐
       ual page), send a mail to

blktrace git-20071207142532   December  8, 2007                  BTREPLAY(8)