blktrace man page on Oracle

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BLKTRACE(8)							   BLKTRACE(8)

       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 ana‐
       lyse 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 con‐
       cerning 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 hexadeci‐
	 mal 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.blk‐
	 trace.cpu, where device is the base device name (e.g, if we are trac‐
	 ing /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 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.

       -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

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

	      Run in network listen mode (blktrace server)

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

       -p number
	      Network port to use (default 8462)

	      Make the network client NOT use sendfile() to transfer data

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

       -D 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
	      Specifies debugfs mount point

	      Outputs 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, mul‐
       tiple 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

       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  Pub‐
       lic 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

blktrace git-20070306202522	March  6, 2007			   BLKTRACE(8)

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