iostat

       put statistics for devices and partitions.

SYNOPSIS
       iostat [ -c ] [ -d ] [ -h ] [ -N ] [ -k | -m ] [ -t ] [ -V ] [ -x  ]  [
       -z ] [ device [...] | ALL ] [ -p [ device [,...] | ALL ] ] [ interval [
       count ] ]

DESCRIPTION
       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. The iostat command generates reports that
       can  be  used  to  change  system  configuration  to better balance the
       input/output load between physical disks.

       The first report generated by the iostat  command  provides  statistics
       concerning the time since the system was booted. Each subsequent report
       covers the time since the previous report. All statistics are  reported
       each  time  the  iostat  command  is  run. The report consists of a CPU
       header row followed by a row of CPU statistics. On multiprocessor  sys-
       tems,  CPU  statistics are calculated system-wide as averages among all
       processors. A device header row is displayed followed by a line of sta-
       tistics for each device that is configured.

       The  interval parameter specifies the amount of time in seconds between
       each report. The first report contains statistics for  the  time  since
       system  startup (boot). Each subsequent report contains statistics col-
       lected during the interval since the previous report. The count parame-
       ter can be specified in conjunction with the interval parameter. If the
       count parameter is specified, the value of count determines the  number
       of reports generated at interval seconds apart. If the interval parame-
       ter is specified without the count parameter, the iostat command gener-
       ates reports continuously.


REPORTS
       The  iostat  command generates three types of reports, the CPU Utiliza-
       tion report, the Device Utilization report and the  Network  Filesystem
       report.

       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.  The report has the fol-
              lowing format:

              %user
                     Show the percentage  of  CPU  utilization  that  occurred
                     while executing at the user level (application).

              %nice
                     Show  the  percentage  of  CPU  utilization that occurred
                     while executing at the user level with nice priority.

              %system

              %idle
                     Show  the  percentage  of  time that the CPU or CPUs were
                     idle and the system did not have an outstanding disk  I/O
                     request.

       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 and parti-
              tions for which statistics are to be displayed may be entered on
              the  command  line.  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.  Transfer rates are shown in 1K
              blocks  by default, unless the environment variable POSIXLY_COR-
              RECT is set, in which case 512-byte blocks are used.  The report
              may show the following fields, depending on the flags used:

              Device:
                     This  column  gives  the  device  (or  partition) name as
                     listed in the /dev directory.

              tps
                     Indicate the number of transfers  per  second  that  were
                     issued to the device. A transfer is an I/O request to the
                     device. Multiple logical requests can be combined into  a
                     single  I/O request to the device. A transfer is of inde-
                     terminate size.

              Blk_read/s (kB_read/s, MB_read/s)
                     Indicate  the  amount  of  data  read  from  the   device
                     expressed  in  a  number of blocks (kilobytes, megabytes)
                     per second. Blocks are equivalent to sectors  and  there-
                     fore have a size of 512 bytes.

              Blk_wrtn/s (kB_wrtn/s, MB_wrtn/s)
                     Indicate  the  amount  of  data  written  to  the  device
                     expressed in a number of  blocks  (kilobytes,  megabytes)
                     per second.

              Blk_read (kB_read, MB_read)
                     The total number of blocks (kilobytes, megabytes) read.

              Blk_wrtn (kB_wrtn, MB_wrtn)
                     The  total  number of blocks (kilobytes, megabytes) writ-
                     ten.

              rrqm/s
                     The number of read requests merged per second  that  were
                     queued to the device.

              rsec/s (rkB/s, rMB/s)
                     The number of sectors (kilobytes,  megabytes)  read  from
                     the device per second.

              wsec/s (wkB/s, wMB/s)
                     The  number  of sectors (kilobytes, megabytes) written to
                     the device per second.

              avgrq-sz
                     The average size (in sectors) of the requests  that  were
                     issued to the device.

              avgqu-sz
                     The average queue length of the requests that were issued
                     to the device.

              await
                     The average  time  (in  milliseconds)  for  I/O  requests
                     issued to the device to be served. This includes the time
                     spent by the requests in queue and the time spent servic-
                     ing them.

              r_await
                     The  average  time  (in  milliseconds)  for read requests
                     issued to the device to be served. This includes the time
                     spent by the requests in queue and the time spent servic-
                     ing them.

              w_await
                     The average time (in  milliseconds)  for  write  requests
                     issued to the device to be served. This includes the time
                     spent by the requests in queue and the time spent servic-
                     ing them.

              svctm
                     The  average  service  time  (in  milliseconds)  for  I/O
                     requests that were issued to the device. Warning! Do  not
                     trust this field any more.  This field will be removed in
                     a future sysstat version.

              %util
                     Percentage of CPU time during  which  I/O  requests  were
                     issued  to  the  device  (bandwidth  utilization  for the
                     device). Device saturation  occurs  when  this  value  is
                     close to 100%.

OPTIONS
       -c     Display the CPU utilization report.

       -d     Display the device utilization report.

       -h     Make the Device Utilization Report easier to read by a human.

       -k     Display statistics in kilobytes per second.
              and  partitions defined by the system, including those that have
              never been used.

       -t     Print the time for each report displayed. The  timestamp  format
              may  depend  on the value of the S_TIME_FORMAT environment vari-
              able (see below).

       -V     Print version number then exit.

       -x     Display extended statistics.

       -z     Tell iostat to omit output for any devices for which  there  was
              no activity during the sample period.


ENVIRONMENT
       The  iostat  command takes into account the following environment vari-
       ables:


       S_TIME_FORMAT
              If this variable exists and its value is ISO  then  the  current
              locale  will  be  ignored  when  printing the date in the report
              header.  The  iostat  command  will  use  the  ISO  8601  format
              (YYYY-MM-DD)  instead.   The  timestamp displayed with option -t
              will also be compliant with ISO 8601 format.


       POSIXLY_CORRECT
              When this variable is set, transfer rates are shown in  512-byte
              blocks instead of the default 1K blocks.


EXAMPLES
       iostat
              Display  a  single  history  since  boot  report for all CPU and
              Devices.

       iostat -d 2
              Display a continuous device report at two second intervals.

       iostat -d 2 6
              Display six reports at two second intervals for all devices.

       iostat -x sda sdb 2 6
              Display six reports of extended statistics at two second  inter-
              vals for devices sda and sdb.

       iostat -p sda 2 6
              Display  six  reports at two second intervals for device sda and
              all its partitions (sda1, etc.)

BUGS
       /proc filesystem must be mounted for iostat to work.

       /proc/diskstats contains disks statistics.

       /sys contains statistics for block devices.

       /proc/self/mountstats contains statistics for network filesystems.

AUTHOR
       Sebastien Godard (sysstat <at> orange.fr)

SEE ALSO
       sar(1), pidstat(1), mpstat(1), vmstat(8), nfsiostat(1), cifsiostat(1)

       http://pagesperso-orange.fr/sebastien.godard/



Linux                              MAY 2011                          IOSTAT(1)
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