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       blktrace - generate traces of the i/o traffic on block devices


       blktrace  -d  dev [ -r debugfs_path ] [ -o output ] [-k ] [ -w time ] [
       -a action ] [ -A action_mask ] [ -v ]


       blktrace is a block layer IO tracing mechanism which provides  detailed
       information  about request queue operations up to user space. There are
       three major components: a kernel component, a utility to record the i/o
       trace  information  for  the  kernel  to  user  space, and utilities to
       analyse and view  the  trace  information.   This  man  page  describes
       blktrace,  which records the i/o event trace information for a specific
       block device to a file.

       The blktrace utility extracts event traces from  the  kernel  (via  the
       relaying  through  the  debug  file  system).  Some  background details
       concerning the run-time behaviour of blktrace will help  to  understand
       some of the more arcane command line options:

       - blktrace  receives  data from the kernel in buffers passed up through
         the debug file system (relay). Each device being traced  has  a  file
         created  in  the mounted directory for the debugfs, which defaults to
         /sys/kernel/debug -- this can be overridden with the -r command  line

       - blktrace  defaults  to  collecting  all events that can be traced. To
         limit the events being captured, you can specify one or  more  filter
         masks via the -a option.

         Alternatively,   one   may   specify  the  entire  mask  utilising  a
         hexadecimal value that is version-specific.  (Requires  understanding
         of the internal representation of the filter mask.)

       - As  noted  above,  the  events  are passed up via a series of buffers
         stored into debugfs files. The size and  number  of  buffers  can  be
         specified via the -b and -n arguments respectively.

       - blktrace  stores  the  extracted  data into files stored in the local
         directory.  The  format  of  the   file   names   is   (by   default)
         device.blktrace.cpu, where device is the base device name (e.g, if we
         are tracing /dev/sda, the base device name would  be  sda);  and  cpu
         identifies a CPU for the event stream.

         The  device  portion of the event file name can be changed via the -o

       - blktrace may also be run concurrently with blkparse to  produce  live
         output -- to do this specify -o - for blktrace.

       - The default behaviour for blktrace is to run forever until explicitly
         killed by the user (via a control-C,  or  kill  utility  invocation).
         There are two ways to modify this:

         1. You  may  utilise  the  blktrace  utility itself to kill a running
            trace -- via the -k option.

         2. You can specify a run-time duration for blktrace via the -w option
            -- then blktrace will run for the specified number of seconds, and
            then halt.


       -A hex-mask
              Set filter mask to hex-mask (see below for masks)

       -a mask
              Add mask to current filter (see below for masks)

       -b size
              Specifies buffer size for event extraction (scaled by 1024). The
              default buffer size is 512KiB.

       -d dev
              Adds dev as a device to trace

       -I file
              Adds the devices found in file as devices to trace

              Kill on-going trace

       -n num-sub
              Specifies  number  of buffers to use. blktrace defaults to 4 sub

       -o file
              Prepend file to output file name(s)

       -r rel-path
              Specifies debugfs mount point

       --version Outputs version

       -w seconds
              Sets run time to the number of seconds specified


       The following masks may be passed with  the  -a  command  line  option,
       multiple  filters may be combined via multiple -a command line options.

              barrier: barrier attribute
              complete: completed by driver
              fs: requests
              issue: issued to driver
              pc: packet command events
              queue: queue operations
              read: read traces
              requeue: requeue operations
              sync: synchronous attribute
              write: write traces
              notify: trace messages


       blktrace distinguishes between two types of block layer requests,  file
       system and SCSI commands. The former are dubbed fs requests, the latter
       pc requests. File system requests  are  normal  read/write  operations,
       i.e.   any  type  of  read  or write from a specific disk location at a
       given size. These requests typically originate from a user process, but
       they may also be initiated by the vm flushing dirty data to disk or the
       file system syncing a super or journal block to disk. pc  requests  are
       SCSI  commands.  blktrace  sends the command data block as a payload so
       that blkparse can decode it.


       To trace the i/o on the device /dev/hda and parse the output  to  human
       readable form, use the following command:

           % blktrace -d /dev/sda -o - | blkparse -i -

       This  same behaviour can be achieve with the convenience script btrace.
       The command

           % btrace /dev/sda

       has exactly the same effect as the previous command. See btrace (8) for
       more information.

       To  trace  the i/o on a device and save the output for later processing
       with blkparse, use blktrace like this:

           % blktrace /dev/sda /dev/sdb

       This will trace i/o on the devices /dev/sda and /dev/sdb and  save  the
       recorded information in the files sda and sdb in the current directory,
       for the two different devices, respectively.   This  trace  information
       can later be parsed by the blkparse utility:

           % blkparse sda sdb

       which  will output the previously recorded tracing information in human
       readable form to stdout.  See blkparse (1) for more information.


       blktrace was written by Jens Axboe, Alan D. Brunelle and Nathan  Scott.
       This  man  page  was  created  from  the  blktrace documentation by Bas


       Report bugs to <>


       Copyright © 2006 Jens Axboe, 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.


       btrace  (8),  blkparse  (1), verify_blkparse (1), blkrawverify (1), btt