Introduction

These instructions have been tested on the following distributions:

• RedHat5.2

And were tested using blktrace version 1.0.1

Please let support@fusionio.com know if you have tested this on any other distributions, as well as what modifications, if any, were needed.

Prerequisites

You will need a 2.6.17 kernel, or greater.

Installation

If not already available for your distribution, download blktrace from:
http://brick.kernel.dk/snaps/

Setup/Running

1. Ensure that debugfs is mounted on /sys/kernel/debug.

$ grep debug /proc/mounts

If debugfs is mounted, you should see:

none /sys/kernel/debug debugfs rw 0 0

If not mounted, mount it.

$ mount -t debugfs none /sys/kernel/debug

3. Capture a 10 minute trace.

$ ./blktrace -d /dev/fioa -w 600

=== fioa ===

  CPU  0:                    0 events,        0 KiB data
  CPU  1:                 1205 events,       57 KiB data
  CPU  2:                  106 events,        5 KiB data
  CPU  3:                    0 events,        0 KiB data
  CPU  4:               573397 events,    26878 KiB data
  CPU  5:                 7059 events,      331 KiB data
  CPU  6:                 4956 events,      233 KiB data
  CPU  7:                21903 events,     1027 KiB data

  Total:                608626 events (dropped 0),    28530 KiB data

The output is stored in several files, one per CPU core, and named after the device traced:

$ ls -al fioa*

-rw-r--r-- 1 root root        0 Jul  8 10:01 fioa.blktrace.0
-rw-r--r-- 1 root root    57856 Jul  8 10:01 fioa.blktrace.1
-rw-r--r-- 1 root root     5088 Jul  8 10:01 fioa.blktrace.2
-rw-r--r-- 1 root root        0 Jul  8 10:01 fioa.blktrace.3
-rw-r--r-- 1 root root 27523072 Jul  8 10:01 fioa.blktrace.4
-rw-r--r-- 1 root root   338856 Jul  8 10:01 fioa.blktrace.5
-rw-r--r-- 1 root root   237920 Jul  8 10:01 fioa.blktrace.6
-rw-r--r-- 1 root root  1051352 Jul  8 10:01 fioa.blktrace.7

Please contact support@fusionio.com for a location to upload a tarball of your tracefiles to for analysis.

Replay capture with fio ( http://freshmeat.net/projects/fio )

1. Convert the multiple blktrace captures to a fio compatable input file.

$ ./blkparse fioa -d trace_input_for_fio -o /dev/null

2. Reference the trace file in the fio job by adding something similar to the following into the fio job file:

read_iolog=trace_input_for_fio