iostat
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 ] [ -t ] [ -V ] [ -x [ device ] ] [ 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 dis played 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 parame ter. If the count parameter is specified, the value of count determines the number of reports generated at inter val 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 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 (application). %nice Show the percentage of CPU utilization that occurred while executing at the user level with nice priority. %sys Show the percentage of CPU utilization that occurred while executing at the system level (kernel). %idle Show the percentage of time that the CPU or CPUs were idle. 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. The report may show the following fields, depending on whether -x option is used or not: Device: This column gives the device name, which is displayed as hdiskn with 2.2 kernels, for the nth device. It is displayed as devm-n with newer kernels, where m is the major number of the device, and n a distinctive number. When -x option is used, the device name as listed in the /dev directory is dis played. 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 sin gle I/O request to the device. A transfer is of indeterminate size. Blk_read/s Indicate the amount of data read from the drive expressed in a number of blocks per second. A block is of indeterminate size. Blk_wrtn/s Indicate the amount of data written to the drive expressed in a number of blocks per second. A block is of indeterminate size. Blk_read The total number of blocks read. Blk_wrtn The total number of blocks written. rrqm/s The number of read requests merged per sec ond that were issued to the device. wrqm/s The number of write requests merged per sec ond that were issued 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. 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. 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.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. -t Print the time for each report displayed. -V Print version number and usage then exit. -x device Display extended statistics. If no device is given on the command line, then extended statistics are displayed for every device registered in the /proc/partitions file. Please note that Linux ker nel needs to be patched for this option to work. ENVIRONMENT The iostat command takes into account the following envi ronment 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 format (YYYY-MM-DD) instead. 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. BUGS Statistics in KB/s for each block device are not available by default due to Linux poor disk accounting. For the same reason, a kernel patch needs to be applied for extended statistics to be displayed. /proc filesystem must be mounted for iostat to work. FILE /proc/stat contains system statisitics. /proc/partitions contains statistics for the devices.AUTHOR
Sebastien Godard <sebastien.godard@wanadoo.fr>SEE ALSO
vmstat(8), sar(1), mpstat(1) http://perso.wanadoo.fr/sebastien.godard/ Linux FEBRUARY 2001 IOSTAT(1)