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How do I find out Linux Disk utilization?

Posted by Vivek on Monday December 17, 07 @2:24 pm

I've already written about finding out Linux / UNIX cpu utilization using various tools. You can use same iostat command to find out disk utilization and for monitoring system input/output device loading by observing the time the physical disks are active in relation to their average transfer rates.

iostat syntax for disk utilization report

iostat -d -x interval count

Display 3 reports of extended statistics at 5 second intervals for disk

Type the following command:
$ iostat -d -x 5 3
Output:

Linux 2.6.18-53.1.4.el5 (moon.nixcraft.in)   12/17/2007

Device:         rrqm/s   wrqm/s   r/s   w/s   rsec/s   wsec/s avgrq-sz avgqu-sz   await  svctm  %util
sda               1.10    39.82  3.41 13.59   309.50   427.48    43.36     0.17   10.03   1.03   1.75
sdb               0.20    18.32  1.15  6.08   117.36   195.25    43.22     0.51   71.14   1.26   0.91

Device:         rrqm/s   wrqm/s   r/s   w/s   rsec/s   wsec/s avgrq-sz avgqu-sz   await  svctm  %util
sda               0.00   108.40  1.40 64.40    49.60  1382.40    21.76     0.04    0.67   0.44   2.92
sdb               0.00    37.80  0.00 245.20     0.00  2254.40     9.19    28.91  108.49   1.08  26.36

Device:         rrqm/s   wrqm/s   r/s   w/s   rsec/s   wsec/s avgrq-sz avgqu-sz   await  svctm  %util
sda               0.00    97.01  1.00 57.29    39.92  1234.33    21.86     0.03    0.58   0.50   2.89
sdb               0.00    38.32  0.00 288.42     0.00  2623.55     9.10    32.97  122.30   1.15  33.27

Where,

How do I interpret the output result for optimization?

First you need to note down following values from the iostat output:

  1. The average service time (svctm)
  2. Percentage of CPU time during which I/O requests were issued (%util)
  3. See if a hard disk reports consistently high reads/writes (r/s and w/s)

If any one of these are high, you need to take one of the following action:

For example, from about iostat report it appears that /dev/sdb under load. Hope this information will help you diagnose and optimize disk related issues.

Related: How to find out Linux CPU utilization using vmstat, iostat, mpstat and sar commands.

Please note that command and information discussed here almost applies to any other UNIX like variant.

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Discussion on This Article:

  1. Rishi kapur Says:

    Please suggest me - system load average is shooting.

    %iowait is high and found with iostat output one disk mentioned below may be the cause.

    Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s rkB/s wkB/s avgrq-sz avgqu-sz await svctm %util
    cciss/c0d0 2269.60 132.60 296.20 77.60 20521.60 1681.60 10260.80 840.80 59.40 4.15 11.18 2.65 99.20

    please suggest

  2. Mike Says:

    When I enter the command “iostat -d -x 5 3″ I do not get any statistics. Here is what I get:

    # iostat -d -x 5 3
    Linux 2.4.33.3 (FILES) 03/01/2008

    Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util

    Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util

    Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util

    Any ideas on what the problem could be? I’m running Slackware 11.0 with the stock kernel.

    Thanks in advance.

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