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

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 ] [ [ [ -T ] -g group_name ] { 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 param-
       eter  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  com-
       mand 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 com-
              mand 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.  Mul-
                     tiple 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.

       -g group_name { device [...] | ALL }
              Display statistics for a group of devices.  The iostat command reports statistics for each individual device in the list then a line
              of global statistics for the group displayed as group_name and made up of all the devices in the list. The ALL  keyword  means  that
              all the block devices defined by the system shall be included in the group.

       -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  sta-
              tistics  have  to  be displayed for all the block devices and partitions defined by the system, including those that have never been
              used.

       -T     This option must be used with option -g and indicates that only global statistics for the group are to be displayed, and not statis-
              tics for individual devices in the group.

       -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/

Linux                                                                MAY 2012                                                            IOSTAT(1)