Provided by: sysstat_11.2.0-1_amd64 bug

NAME

       iostat  -  Report Central Processing Unit (CPU) statistics and input/output statistics for
       devices and partitions.

SYNOPSIS

       iostat [ -c ] [ -d ] [ -h ] [ -k | -m ] [ -N ] [ -t ] [ -V ] [ -x ] [ -y ] [ -z ] [  -j  {
       ID | LABEL | PATH | UUID | ... } ] [ [ -H ] -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
       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  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 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 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% for devices serving requests serially.  But  for
                     devices  serving  requests in parallel, such as RAID arrays and modern SSDs,
                     this number does not reflect their performance limits.

OPTIONS

       -c     Display the CPU utilization report.

       -d     Display the device utilization report.

       -g group_name { device [...] | ALL }
              Display statistics for a group of devices.  The iostat command  reports  statistics
              for  each  individual  device  in the list then a line of global statistics for the
              group displayed as group_name and made up of all the devices in the list.  The  ALL
              keyword means that all the block devices defined by the system shall be included in
              the group.

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

       -j { ID | LABEL | PATH | UUID | ... } [ device [...] | ALL ]
              Display persistent device names. Options ID, LABEL, etc. specify the  type  of  the
              persistent name. These options are not limited, only prerequisite is that directory
              with required persistent names  is  present  in  /dev/disk.   Optionally,  multiple
              devices  can  be  specified in the chosen persistent name type.  Because persistent
              device names are usually long, option

       -H     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.  -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     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.

       -y     Omit first report with statistics since system boot, if displaying 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 variables:

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

       S_COLORS
              When  this  variable is set, display statistics in color on the terminal.  Possible
              values for this variable are never, always or auto (the latter is the default).

              Please note that the color (being red, yellow, or some other color) used to display
              a value is not indicative of any kind of issue simply because of the color. It only
              indicates different ranges of values.

       S_COLORS_SGR
              Specify the colors and other attributes used to display statistics on the terminal.
              Its   value   is   a   colon-separated   list  of  capabilities  that  defaults  to
              H=31;1:I=32;22:M=34;1:N=33;1:Z=33;22.  Supported capabilities are:

              H=     SGR (Select Graphic Rendition) substring for percentage values greater  than
                     or equal to 75%.

              I=     SGR substring for device names.

              M=     SGR substring for percentage values in the range from 50% to 75%.

              N=     SGR substring for non-zero statistics values.

              Z=     SGR substring for zero values.

       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.

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  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), tapestat(1), nfsiostat(1), cifsiostat(1)

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