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



NAME
       iostat  -  Report  Central Processing Unit (CPU) statistics and input/output statistics for devices, partitions
       and network filesystems (NFS).

SYNOPSIS
       iostat [ -c ] [ -d ] [ -N ] [ -n ] [ -h ] [ -k | -m ] [ -t ] [ -V ] [ -x ] [ -y ] [ -z ] [ -j { ID  |  LABEL  |
       PATH | UUID | ... } [ device [...] | ALL ] ] [ 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, unless the -y option is used, when this first report is omitted. 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 calcu-
       lated 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.  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), unless the -y option is used, when this report is omitted.
       Each subsequent report contains statistics collected during the interval since the previous report.  The  count
       parameter 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 command 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  sys-
              tems, 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 (applica-
                     tion).

              %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 (ker-
                     nel).

              %iowait
                     Show the percentage of time that the CPU or CPUs were idle during which the system  had  an  out-
                     standing disk I/O request.

              %steal
                     Show the percentage of time spent in involuntary wait by the virtual CPU or CPUs while the hyper-
                     visor 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  out-
                     standing 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
              providing that option -x is not used.  If no device nor partition is entered, then statistics  are  dis-
              played  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 indeterminate 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 servicing them.

              svctm
                     The average service time (in milliseconds) for I/O requests that were issued to the device. Warn-
                     ing! Do not trust this field any more. This field will be removed in a future sysstat version.

              %util
                     Percentage  of  elapsed  time during which I/O requests were issued to the device (bandwidth uti-
                     lization 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 followed by a colon and by the directory name
                     where the network 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.

       -j { ID | LABEL | PATH | UUID | ... } [ device [...] | ALL ]
              Display  persistent device names. Options ID, LABEL, etc. specify the type of the persistent name. These
              options are not limited, only prerequisite is that directory with required persistent names  is  present
              in /dev/disk.  Optionally, multiple devices can be specified in the chosen persistent name type.

       -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 kernels 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  sys-
              tem.  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. If option -j is
              defined before this option, devices entered on the command line can be specified with the chosen persis-
              tent name type.  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 variable (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 kernels (e.g. 2.4)
              only if extended statistics are available in /proc/partitions (the kernel needs to be patched for that).

       -y     Omit  first report with statistics since the system boot, if displaying multiple records in given inter-
              val.

       -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 variable:


       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 intervals 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.

       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/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.

       /dev/disk contains persistent device names.

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

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

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



Linux                             APRIL 2009                         IOSTAT(1)