BLKTRACE(8)															       BLKTRACE(8)

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  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
	 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 speci-
	 fied 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 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 blk-
	 trace 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 pay-
       load 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 direc-
       tory, 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 (C) 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)

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