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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, partitions and network filesystems (NFS).

SYNOPSIS
       iostat [ -c ] [ -d ] [ -N ] [ -n ] [ -h ] [ -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  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.  When option -n is used, an
       NFS header row is displayed followed by a line of statistics  for  each
       network filesystem that is mounted.

       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 three types of reports, the CPU Utiliza‐
       tion report, the Device Utilization report and the  Network  Filesystem
       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 and parti‐
	      tions 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.	The report may show  the  fol‐
	      lowing 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	 kernels  2.4  and  later  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%.

       Network Filesystem report
	      The Network Filesystem (NFS) report provides statistics for each
	      mounted  network	filesystem.   The  report  shows the following
	      fields:

	      Filesystem:
		     This columns shows the hostname of the  NFS  server  fol‐
		     lowed by a colon and by the directory name where the net‐
		     work filesystem is mounted.

	      rBlk_nor/s
		     Indicate the number of blocks read	 by  applications  via
		     the  read(2) system call interface. A block has a size of
		     512 bytes.

	      wBlk_nor/s
		     Indicate the number of blocks written by applications via
		     the write(2) system call interface.

	      rBlk_dir/s
		     Indicate the number of blocks read from files opened with
		     the O_DIRECT flag.

	      wBlk_dir/s
		     Indicate the number of blocks  written  to	 files	opened
		     with the O_DIRECT flag.

	      rBlk_svr/s
		     Indicate the number of blocks read from the server by the
		     NFS client via an NFS READ request.

	      wBlk_svr/s
		     Indicate the number of blocks written to  the  server  by
		     the NFS client via an NFS WRITE request.

	      rkB_nor/s
		     Indicate the number of kilobytes read by applications via
		     the read(2) system call interface.

	      wkB_nor/s
		     Indicate the number of kilobytes written by  applications
		     via the write(2) system call interface.

	      rkB_dir/s
		     Indicate  the  number of kilobytes read from files opened
		     with the O_DIRECT flag.

	      wkB_dir/s
		     Indicate the number of kilobytes written to files	opened
		     with the O_DIRECT flag.

	      rkB_svr/s
		     Indicate  the number of kilobytes read from the server by
		     the NFS client via an NFS READ request.

	      wkB_svr/s
		     Indicate the number of kilobytes written to the server by
		     the NFS client via an NFS WRITE request.

	      rMB_nor/s
		     Indicate the number of megabytes read by applications via
		     the read(2) system call interface.

	      wMB_nor/s
		     Indicate the number of megabytes written by  applications
		     via the write(2) system call interface.

	      rMB_dir/s
		     Indicate  the  number of megabytes read from files opened
		     with the O_DIRECT flag.

	      wMB_dir/s
		     Indicate the number of megabytes written to files	opened
		     with the O_DIRECT flag.

	      rMB_svr/s
		     Indicate  the number of megabytes read from the server by
		     the NFS client via an NFS READ request.

	      wMB_svr/s
		     Indicate the number of megabytes written to the server by
		     the NFS client via an NFS WRITE request.

	      ops/s
		     Indicate the number of operations that were issued to the
		     filesystem per second.

	      rops/s
		     Indicate the number of 'read' operations that were issued
		     to the filesystem per second.

	      wops/s
		     Indicate  the  number  of	'write'	 operations  that were
		     issued to the filesystem per second.

OPTIONS
       -c     Display the CPU utilization report.

       -d     Display the device utilization report.

       -h     Make the NFS report displayed by option -n easier to read	 by  a
	      human.

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

       -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 later.

       -N     Display the registered device mapper names for any device mapper
	      devices.	Useful for viewing LVM2 statistics.

       -n     Display the network filesystem (NFS) report. This	 option	 works
	      only with kernel 2.6.17 and later.

       -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.	Note that this option works only with post 2.5
	      kernels.

       -t     Print the time for each report displayed. The  timestamp	format
	      may  depend  on the value of the S_TIME_FORMAT environment vari‐
	      able (see below).

       -V     Print version number then exit.

       -x     Display extended statistics.  This option 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 ker‐
	      nels  (e.g.  2.4)	 only  if extended statistics are available in
	      /proc/partitions (the kernel needs to be patched for that).

       -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 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.	 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 inter‐
	      vals 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.

       Extended statistics are available only with post 2.5 kernels.

FILES
       /proc/stat contains system statistics.

       /proc/uptime contains system uptime.

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

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

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

       /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)

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

Linux				 DECEMBER 2009			     IOSTAT(1)
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