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    Reference - IOSTAT
    Brett Lee
    The iostat command produces two reports:
      CPU Utilization Report
      Device Utilization Report
    The information comes from:
           /proc/stat      - system statistics
           /proc/diskstats - disk statistics 
           /proc/uptime    - uptime statistics
           /sys            - block device statistics
    The iostat command is used for monitoring system input/output device loading
    by observing the time the devices are active in relation to their average
    transfer rates.  That's important, so you might want to re-read it.
    If high CPU usage rates are seen and low IO transfer rates are seen, this
    could indicate a problem.  But...
    First of all, the terms "high" and "low" are relative.  In order to be
    accurate, these terms need to be relative to the *expected* I/O of each
    Second, applications have varying disk data access patterns:  sequential,
    random, or a combination of the two.  As is well known, sequential is faster
    than random, for example:  Sequential reads may be ten (10) times as fast as
    random reads, while sequential writes may be five (5) times as fast as random
    writes.  There is an interesting twist to this, in that sequential reads may be
    50% faster than sequential writes, but random reads may be 50% *SLOWER* than
    random writes.
      CPU Utilization Report
             The first report generated by the iostat command is the CPU Uti-
             lization Report. For multiprocessor systems, the CPU values are
             global averages among all processors.
      Device Utilization Report
             The second report generated by the iostat command is the Device
             Utilization Report. The device report provides statistics on a
             per physical device or partition basis. Block devices for which
             statistics are to be displayed may be entered on the command
             line. Partitions may also be entered on the command line provid-
             ing that option -x is not used. If no device nor partition is
             entered, then statistics are displayed for every device used by
             the system, and providing that the kernel  maintains  statistics
             for it.  If the ALL keyword is given on the command line, then
             statistics are displayed for every device defined by the system,
             including those that have never been used. The report may show
             the following fields, depending on the flags used:
           iostat [ -c | -d ] [ -k | -m ] [ -t ] [ -V ] [ -x ] [ -n ]  [  -h  ]  [
           device [ ... ] | ALL ] [ -p [ device | ALL ] ] [ interval [ count ] ]
    -c     ** CPU utilization
           avg-cpu:  %user   %nice %system %iowait  %steal   %idle
                      0.82    0.00    8.44    1.01    0.00   89.74
    -d     **  DISK utilization (in blocks)
           Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
           sda              16.08        23.01       222.79  337915250 3272454414
    -k     **  Both CPU and DISK utilization (in kB)
    -m     **  Both CPU and DISK utilization (in MB)
    -t     **  Both CPU and DISK utilization (in blocks) - timestamped
    -x     **  Both CPU and DISK utilization (in detail) - exclusive of -p and -n
    -n     **  Both CPU and DISK and NFS utilization (in blocks)
    -h     **  Both CPU and DISK and NFS utilization (NFS should be human readable)
               However, I see no difference...
    -p     **  Both CPU and DISK utilization (devices **and** disk partitions)
               `iostat -p sda sdb` shows: sda, sda1, sda2, sdb, sdb1, ...
    For a list of the fields displayed as well as their meaning, please consult
    the man page.

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  • This site contains many of my notes from research into different aspects of the Linux kernel as well as some of the software provided by GNU and others. Thouugh these notes are not fully comprehensive or even completetly accurate, they are part of my on-going attempt to better understand this complex field. And, they are your to use.

    Should you wish to report any errors or suggestions, please let me know.

    Should you wish to make a donation for anything you may have learned here, please direct that donation to the ASPCA, with my sincere thanks.

    Brett Lee
    Everything Penguin

    The code for this site, which is just a few CGI scripts, may be found on GitHub (https://github.com/userbrett/cgindex).

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