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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  ]  [	 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 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  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 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. 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 is exclusive of the -p
	      one,  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.  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 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.

       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				   JULY 2008			     IOSTAT(1)
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