Provided by: sysstat_10.0.3-1_i386 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/