Provided by: sysstat_11.6.1-1_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 ] [ -s ] [ -t ] [ -V ] [ -x ] [ -y ] [ -z ] [
       -j { ID | LABEL | PATH | UUID | ... } ] [ -o JSON ] [ [ -H ] -g group_name ] [ --human ] [
       -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.

              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.

              sec/s (kB/s, MB/s)
                     The  number  of  sectors  (kilobytes, megabytes) read from or written to the
                     device per second.

              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.

              rqm/s
                     The number of I/O requests merged per second that were queued to the device.

              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.

              %rrqm
                     The percentage of read requests merged together before  being  sent  to  the
                     device.

              %wrqm
                     The  percentage  of  write requests merged together before being sent to the
                     device.

              areq-sz
                     The average size (in kilobytes) of the I/O requests that were issued to  the
                     device.
                     Note:  In  previous  versions,  this  field  was  known  as avgrq-sz and was
                     expressed in sectors.

              rareq-sz
                     The average size (in kilobytes) of the read requests that were issued to the
                     device.

              wareq-sz
                     The  average  size  (in kilobytes) of the write 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.

              aqu-sz
                     The average queue length of the requests that were issued to the device.
                     Note: In previous versions, this field was known as avgqu-sz.

              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     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     Make the Device Utilization Report easier to read by a human.  --human  is  enabled
              implicitly with this option.

       --human
              Print  sizes  in  human readable format (e.g. 1k, 1.23M, etc.)  The units displayed
              with this option supersede any other default units  (e.g.   kilobytes,  sectors...)
              associated with the metrics.

       -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

       -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.

       -o JSON
              Display the statistics in JSON (Javascript Object Notation)  format.   JSON  output
              field order is undefined, and new fields may be added in the future.

       -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.

       -s     Display  a  short  (narrow)  version of the report that should fit in 80 characters
              wide screens.

       -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=35;1:N=34;1:Z=34;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/