NAME

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

SYNOPSIS

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

DESCRIPTION

       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 argument.

       - 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 option.

       - 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 sending SIGINT signal to the process via invocation the kill (1)
         utility). Also 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.

OPTIONS

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

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

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

       -d dev
       --dev=dev
              Adds dev as a device to trace

       -I file
       --input-devs=file
              Adds the devices found in file as devices to trace

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

       -l
       --listen
              Run in network listen mode (blktrace server)

       -h hostname
       --host=hostname
              Run in network client mode, connecting to the given host

       -p number
       --port=number
              Network port to use (default 8462)

       -s
       --no-sendfile
              Make the network client NOT use sendfile() to transfer data

       -o basename
       --output=basename
              Specifies base name for input files. Default is device.blktrace.cpu.  Specifying -o
              - runs in live mode with blkparse (writing data to standard out).

       -D dir
       --output-dir=dir
              Prepend file to output file name(s)

              This  only  works when supplying a single device, or when piping the output via "-o
              -" with multiple devices.

       -r rel-path
       --relay=rel-path
              Specifies debugfs mount point

       -v
       --version
              Outputs version

       -V
       --version
              Outputs version

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

FILTER MASKS

       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
              drv_data: additional driver specific trace

REQUEST TYPES

       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.

EXAMPLES

       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.

AUTHORS

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

REPORTING BUGS

       Report bugs to <linux-btrace@vger.kernel.org>

COPYRIGHT

       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 <http://www.gnu.org/licenses/gpl.html>.  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

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