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
the only traces you are interested in are QUEUE requests —
thus, to save system resources (including storage for traces),
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
Set number of CPUs to use.
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.
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
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
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,
'/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:
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.
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
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.
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 email@example.com] It is not known how
to report bugs for this man page; if you know, please send a mail to
firstname.lastname@example.org. This page was obtained from the project's
upstream Git repository
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 email@example.com
blktrace git-20071207142532 December 8, 2007 BTREPLAY(8)