Provided by: sysstat_10.0.3-1_amd64 bug

NAME

       iostat  -  Report Central Processing Unit (CPU) statistics and input/output 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
       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). Each subsequent
       report contains statistics collected during the interval since the  previous  report.  The
       count  parameter 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  parameter  is  specified  without  the count
       parameter, the iostat command generates reports continuously.

REPORTS

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

       CPU Utilization Report
              The first report generated by the iostat command is the CPU Utilization Report. For
              multiprocessor systems, the CPU values are global averages  among  all  processors.
              The report has the following 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
                     Show  the percentage of CPU utilization that occurred while executing at the
                     system level (kernel).

              %iowait
                     Show the percentage of time that the CPU or CPUs were idle during which  the
                     system had an outstanding disk I/O request.

              %steal
                     Show  the percentage of time spent in involuntary wait by the virtual CPU or
                     CPUs while the hypervisor was servicing 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  partitions  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_CORRECT 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
                     indeterminate 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 therefore 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) written.

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

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

              r/s
                     The number (after merges) of read requests  completed  per  second  for  the
                     device.

              w/s
                     The  number  (after  merges)  of write requests completed per second for 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 servicing 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 servicing 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 servicing 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.

       -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.

       -t     Print the time for each report displayed. The timestamp format may  depend  on  the
              value of the S_TIME_FORMAT environment variable (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 variables:

       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 intervals 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
       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.

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/