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iostat



SYNOPSIS

       iostat [ -c ] [ -d ] [ -h ] [ -k | -m ] [ -N ] [ -t ] [ -V ] [ -x  ]  [
       -y  ]  [  -z  ]  [  -j { ID | LABEL | PATH | UUID | ... } ] [ [ -T ] -g
       group_name ] [ -p [ device [,...] | ALL ] ] [ 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, unless the  -y  option
       is  used (in this case, this first report is omitted).  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
       systems,  CPU  statistics  are calculated system-wide as averages among
       all processors. A device header row is displayed followed by a line  of
       statistics 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), unless the -y option is used (in this case, this
       report is omitted).  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 two types of reports, the CPU  Utilization
       report and the Device Utilization 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
                     ing another virtual processor.

              %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

              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 elapsed 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.

              names is present in /dev/disk.  Optionally, multiple devices can
              be specified in the chosen persistent name type.   Because  per-
              sistent  device  names  are  usually  long, option -h is enabled
              implicitly with this option.

       -k     Display statistics in kilobytes per second.

       -m     Display statistics in megabytes per second.

       -N     Display the registered device mapper names for any device mapper
              devices.  Useful for viewing LVM2 statistics.

       -p [ { device [,...] | ALL } ]
              The  -p  option  displays  statistics  for block devices and all
              their partitions that are used by the system.  If a device  name
              is  entered  on the command line, then statistics for it and all
              its partitions are displayed. Last, the  ALL  keyword  indicates
              that  statistics  have to be displayed for all the block devices
              and partitions defined by the system, including those that  have
              never  been  used.  If  option -j is defined before this option,
              devices entered on the command line can be  specified  with  the
              chosen persistent name type.

       -T     This  option must be used with option -g and indicates that only
              global statistics for the group are to  be  displayed,  and  not
              statistics for individual devices in the group.

       -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.

       -y     Omit first report with statistics since system boot, if display-
              ing multiple records at given interval.

       -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
              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.

       Kernels older than 2.6.x are no longer supported.

       The average service time (svctm field) value  is  meaningless,  as  I/O
       statistics  are  now  calculated at block level, and we don't know when
       the disk driver starts to process a  request.  For  this  reason,  this
       field will be removed in a future sysstat version.


FILES

       /proc/stat contains system statistics.

       /proc/uptime contains system uptime.

       /proc/diskstats contains disks statistics.

       /sys contains statistics for block devices.

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

       /dev/disk contains persistent device names.


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 NOVEMBER 2012 IOSTAT(1)



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