IOSTAT - Checking Disk Performance
The iostat command is used for monitoring system input/output device loading by observing the time the physical disks are active in relation to their average transfer rates. It is similar both in format and in use to the vmstat command. The first line of iostat reflects a summary of statistics since boot time. 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 tty and CPU header row followed by a row of tty and CPU statistics.
iostat 10 5
When this command is ran iostat will spend 10 seconds gathering data and reports a single line of statistics. This will continue 5 times. At least 5 seconds is needed for good accuracy.
extended disk statistics tty cpu
disk r/s w/s Kr/s Kw/s wait actv svc_t %w %b tin tout us sy wt id
sd0 2.6 3.0 20.7 22.7 0.1 0.2 59.2 6 19 0 84 3 85 11 0
sd1 4.2 1.0 33.5 8.0 0.0 0.2 47.2 2 23
sd2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0
sd3 10.2 1.6 51.4 12.8 0.1 0.3 31.2 3 31
A description of the information reported is:
* disk: Disk device name.
* r/s, w/s: Average reads/writes per second.
* Kr/s, Kw/s: Average Kb read/written per second.
* wait: Time spent by a process while waiting for block
* (eg disk) I/O to complete. actv: Number of active requests in the hardware queue.
* %w: Occupancy of the wait queue.
* %b: Occupancy of the active queue with the device busy.
* svc_t: Service time (ms). Includes everything: wait time, active queue time, seek rotation, transfer time.
* us/sy: User/system CPU time (%).
* wt: Wait for I/O (%).
* id: Idle time (%).
With this information in hand an Admin can go about tuning the environment to better suit the needs of the business. There are some good tutorials on tuning and interpreting the results at the Princeton University site, Admins choice site, the softlookup site, and (I know this is for an AIX system but the same ideas will apply here as well) the AIX performance Tuning guide.
*********************************** UPDATE ********************
The systat home page can be found here. With this utility comes the iostat and some other utilities for monitoring Linux.
iostat 10 5
When this command is ran iostat will spend 10 seconds gathering data and reports a single line of statistics. This will continue 5 times. At least 5 seconds is needed for good accuracy.
extended disk statistics tty cpu
disk r/s w/s Kr/s Kw/s wait actv svc_t %w %b tin tout us sy wt id
sd0 2.6 3.0 20.7 22.7 0.1 0.2 59.2 6 19 0 84 3 85 11 0
sd1 4.2 1.0 33.5 8.0 0.0 0.2 47.2 2 23
sd2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0
sd3 10.2 1.6 51.4 12.8 0.1 0.3 31.2 3 31
A description of the information reported is:
* disk: Disk device name.
* r/s, w/s: Average reads/writes per second.
* Kr/s, Kw/s: Average Kb read/written per second.
* wait: Time spent by a process while waiting for block
* (eg disk) I/O to complete. actv: Number of active requests in the hardware queue.
* %w: Occupancy of the wait queue.
* %b: Occupancy of the active queue with the device busy.
* svc_t: Service time (ms). Includes everything: wait time, active queue time, seek rotation, transfer time.
* us/sy: User/system CPU time (%).
* wt: Wait for I/O (%).
* id: Idle time (%).
With this information in hand an Admin can go about tuning the environment to better suit the needs of the business. There are some good tutorials on tuning and interpreting the results at the Princeton University site, Admins choice site, the softlookup site, and (I know this is for an AIX system but the same ideas will apply here as well) the AIX performance Tuning guide.
*********************************** UPDATE ********************
The systat home page can be found here. With this utility comes the iostat and some other utilities for monitoring Linux.
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