IOSTATSection: Linux User's Manual (1)Updated: JUNE 2004 |
NAME
iostat - Report Central Processing Unit (CPU) statistics and input/output statistics for devices and partitions.SYNOPSIS
iostat [ -c | -d ] [ -k ] [ -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 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 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 two types of reports, the CPU Utilization report and the Device Utilization 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).
- Show the percentage of CPU utilization that occurred while executing at the user level with nice priority.
- Show the percentage of CPU utilization that occurred while executing at the system level (kernel).
- Show the percentage of time that the CPU or CPUs were idle during which the system had an outstanding disk I/O request.
- 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 providing 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.
-
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.
-
Indicate the amount of data read from the drive expressed in a number of
blocks per second. Blocks are equivalent to sectors with 2.4 kernels and newer
and therefore have a size of 512 bytes. With older kernels, a block is of
indeterminate size.
-
Indicate the amount of data written to the drive expressed in a number of
blocks per second.
-
The total number of blocks read.
-
The total number of blocks written.
-
Indicate the amount of data read from the drive expressed in kilobytes
per second. Data displayed are valid only with kernels 2.4 and newer.
-
Indicate the amount of data written to the drive expressed in kilobytes
per second. Data displayed are valid only with kernels 2.4 and newer.
-
The total number of kilobytes read. Data displayed are valid only with
kernels 2.4 and newer.
-
The total number of kilobytes written. Data displayed are valid only with
kernels 2.4 and newer.
-
The number of read requests merged per second that were issued to the device.
-
The number of write requests merged per second that were issued to the device.
-
The number of read requests that were issued to the device per second.
-
The number of write requests that were issued to the device per second.
-
The number of sectors read from the device per second.
-
The number of sectors written to the device per second.
-
The number of kilobytes read from the device per second.
-
The number of kilobytes written to the device per second.
-
The average size (in sectors) of the requests that were issued to the device.
-
The average queue length of the requests that were issued to the device.
-
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.
-
The average service time (in milliseconds) for I/O requests that were issued
to the device.
- 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%.
-
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.
-
OPTIONS
- -c
- The -c option is exclusive of the -d option and displays only the CPU usage report.
- -d
- The -d option is exclusive of the -c option and displays only the device utilization report.
- -k
- Display statistics in kilobytes per second instead of blocks per second. Data displayed are valid only with kernels 2.4 and newer.
- -p device | ALL
- The -p option is exclusive of the -x option and 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.
- -V
- Print version number and usage 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 kernel
needs to be patched for that).
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.
EXAMPLES
iostat-
Display a single history since boot report for all CPU and Devices.
-
Display a continuous device report at two second intervals.
-
Display six reports at two second intervals for all devices.
-
Display six reports of extended statistics at two second intervals for devices
hda and hdb.
- 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.
Because of what seems to be a Linux kernel bug, iostat -x may display huge I/O response times (svctm) and a bandwidth utilization (%util) of 100% for some devices. Indeed these devices have a value for the field #9 in /proc/{partitions,diskstats} which is always different from 0, and even negative sometimes. Yet this field should go to zero, since it gives the number of I/Os currently in progress (it is incremented as requests are submitted, and decremented as they finish).
FILES
/proc/stat contains system statistics./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).
AUTHOR
Sebastien Godard (sysstat <at> wanadoo.fr)SEE ALSO
sar(1), mpstat(1), vmstat(8)http://perso.wanadoo.fr/sebastien.godard/