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       btreplay - recreate IO loads recorded by blktrace


       btreplay [ options ] <dev...>


       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.
           the only traces you are interested in are QUEUE requests —
           thus,  to save system resources (including storage for traces), one
           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


       -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:

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

              2.  btrecord base name — by default ‘‘replay’’.

              3.  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 value.

       -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
                  ’/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.

              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

              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.


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


       Report bugs to <>


       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.


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