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IOSTAT(1)		      Linux User's Manual		     IOSTAT(1)

NAME
       iostat - Report Central Processing Unit (CPU) statistics and input/out‐
       put statistics for devices and partitions.

SYNOPSIS
       iostat [ -c | -d ] [ -k | -m ] [ -t ] [ -V ] [ -x ] [ -n ]  [  -h  ]  [
       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 sys‐
       tems, CPU statistics are calculated system-wide as averages  among  all
       processors. A device header row is displayed followed by a line of sta‐
       tistics 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  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
		     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  servic‐
		     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 for which
	      statistics are to be displayed may be  entered  on  the  command
	      line. Partitions may also be entered on the command line provid‐
	      ing that option -x is not used.  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.  The report may show
	      the following fields, depending on the flags used:

	      Device:
		     This column gives the device (or partition)  name,	 which
		     is	 displayed  as	hdiskn	with  2.2 kernels, for the nth
		     device. It is displayed as devm-n with 2.4 kernels, where
		     m	is the major number of the device, and n a distinctive
		     number.  With newer kernels, the device name as listed in
		     the /dev directory is displayed.

	      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
		     Indicate	the  amount  of	 data  read  from  the	device
		     expressed in a number of blocks per  second.  Blocks  are
		     equivalent	 to  sectors  with  2.4	 kernels and newer and
		     therefore have a size of 512 bytes. With older kernels, a
		     block is of indeterminate size.

	      Blk_wrtn/s
		     Indicate  the  amount  of	data  written  to  the	device
		     expressed in a number of blocks per second.

	      Blk_read
		     The total number of blocks read.

	      Blk_wrtn
		     The total number of blocks written.

	      kB_read/s
		     Indicate  the  amount  of	data  read  from  the	device
		     expressed in kilobytes per second.

	      kB_wrtn/s
		     Indicate  the  amount  of	data  written  to  the	device
		     expressed in kilobytes per second.

	      kB_read
		     The total number of kilobytes read.

	      kB_wrtn
		     The total number of kilobytes written.

	      MB_read/s
		     Indicate  the  amount  of	data  read  from  the	device
		     expressed in megabytes per second.

	      MB_wrtn/s
		     Indicate  the  amount  of	data  written  to  the	device
		     expressed in megabytes per second.

	      MB_read
		     The total number of megabytes read.

	      MB_wrtn
		     The total number of 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 of read	 requests  that	 were  issued  to  the
		     device per second.

	      w/s
		     The  number  of  write  requests  that were issued to the
		     device per second.

	      rsec/s
		     The number of sectors read from the device per second.

	      wsec/s
		     The number of sectors written to the device per second.

	      rkB/s
		     The number of kilobytes read from the device per second.

	      wkB/s
		     The number of kilobytes written to the device per second.

	      rMB/s
		     The number of megabytes read from the device per second.

	      wMB/s
		     The number of 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.

	      svctm
		     The  average  service  time  (in  milliseconds)  for  I/O
		     requests that were issued to the device.

	      %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%.

	      rops/s
		     Indicate  the  number of read operations that were issued
		     to the mount point per second

	      wops/s
		     Indicate the number of write operations that were	issued
		     to the mount point per second

OPTIONS
       -c     The  -c  option  is exclusive of the -d option and displays only
	      the CPU usage report.

       -d     The -d option is exclusive of the -c option  and	displays  only
	      the device utilization report.

       -k     Display statistics in kilobytes per second instead of blocks per
	      second.  Data displayed are valid	 only  with  kernels  2.4  and
	      newer.

       -m     Display  statistics in megabytes per second instead of blocks or
	      kilobytes per second.  Data displayed are valid only  with  ker‐
	      nels 2.4 and newer.

       -n     Displays	the NFS-directory statistic.  Data displayed are valid
	      only with kernels 2.6.17 and newer.  This option is exclusive ot
	      the -x option.

       -h     Display the NFS report more human readable.

       -p [ { device | ALL } ]
	      The -p option is exclusive of the -x option and displays statis‐
	      tics 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 dis‐
	      played for all the block devices and partitions defined  by  the
	      system,  including  those	 that have never been used.  Note that
	      this option works only with post 2.5 kernels.

       -t     Print the time for each report displayed.

       -V     Print version number then exit.

       -x     Display extended statistics.  This option is exclusive of the -p
	      and  -n,	and  works  with  post	2.5  kernels  since  it	 needs
	      /proc/diskstats file or a mounted sysfs to get  the  statistics.
	      This  option may also work with older kernels (e.g. 2.4) only if
	      extended statistics are available in /proc/partitions (the  ker‐
	      nel needs to be patched for that).

ENVIRONMENT
       The  iostat  command takes into account the following environment vari‐
       able:

       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.

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 hda hdb 2 6
	      Display six reports of extended statistics at two second	inter‐
	      vals for devices hda and hdb.

       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.

       On SMP machines iostat assumes that CPU #0 is  never  disabled.	Indeed
       iostat uses it to calculate the time interval.

       Extended statistics are available only with post 2.5 kernels.

FILES
       /proc/stat contains system statistics.

       /proc/partitions	 contains  disk	 statistics  (for pre 2.5 kernels that
       have been patched).

       /proc/diskstats contains disks statistics (for post 2.5 kernels).

       /proc/uptime contains system uptime in seconds  and  centiseconds  (for
       post 2.5 kernels).

       /sys contains statistics for block devices (post 2.5 kernels).

AUTHOR
       Sebastien Godard (sysstat <at> wanadoo.fr)

SEE ALSO
       sar(1), mpstat(1), vmstat(8)

       http://perso.orange.fr/sebastien.godard/

Linux				 OCTOBER 2006			     IOSTAT(1)
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