Install blktrace on Debian based systems:
root@host:~# apt-get install blktrace
Ensure that the virtual filesystem Debug-FS is mounted:
root@host:~# mount | grep debugfs
Mount the Debug-FS if it's currently not available:
root@host:~# /etc/init.d/mountdebugfs start
or:
root@host:~# mount -t debugfs debugfs /sys/kernel/debug
Start the recording of the block I/O on a device until CTRL+Ctrl is pressed. In this example the block device /dev/sda:
root@host:~# blktrace /dev/sda ^C === sda === CPU 0: 8674 events, 407 KiB data CPU 1: 9747 events, 457 KiB data CPU 2: 631 events, 30 KiB data CPU 3: 8977 events, 421 KiB data Total: 28029 events (dropped 0), 1314 KiB data
This creates the output files sda.blktrace.<CPU-#> in the current working directory. The output files can be analysed with the command:
root@host:~# blkparse -i sda.blktrace.<CPU-#>
See man blkparse for a description of the output format.
Recording and analysis of the block I/O on a device can be pipelined:
root@host:~# blktrace /dev/sda -o - | blkparse -i -
or the shorthand command:
root@host:~# btrace /dev/sda
be used.
To record and replay the block I/O on a device the commands btrecord and btreplay can be used. This can be especially useful to compare different environments or settings with the exact same block I/O load.
The tool btt perfoms an analysis on the output files written by the blktrace command:
root@host:~# btt -i sda.blktrace.0
See man btt for the available options.
The tool blkiomon can be used to perfom an iostat-like analysis on the output generated by the blktrace command. For example to generate an 1 hour long trace of the device /dev/sda and output the statistics in a human-readable format in 10 second intervals:
root@host:~# blktrace /dev/sda -w 3600 -o - | blkiomon -I 10 -h -
See man blkiomon for the available options.
For visualization purposes there are the tools bno_plot and iowatcher available.