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    Command:

    iostat

    
    
    
    

    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  sys-
           tems,  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 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.
    
                  %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.  Transfer rates are shown in 1K
                  blocks  by default, unless the environment variable POSIXLY_COR-
                  RECT 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 inde-
                         terminate 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  there-
                         fore 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) writ-
                         ten.
    
                  rrqm/s
                         The number of read requests merged per second  that  were
                         queued to the device.
                         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 servic-
                         ing 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 servic-
                         ing 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 servic-
                         ing 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.
    
                  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 vari-
                  able (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 vari-
           ables:
    
           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  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/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/
    
    
    

    Linux MAY 2011 IOSTAT(1)

    
    
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