How to Check Disk Activity (sar -d) (System Administration Guide: Advanced Administration)

System Administration Guide: Advanced Administration

How to Check Disk Activity (`sar -d`)

Display disk activity statistics with the sar -d command.

$ sar -d

00:00:00   device        %busy   avque   r+w/s  blks/s  avwait  avserv

Example 13–7 Checking Disk Activity

This abbreviated example illustrates the output from the sar -d command.

$ sar -d

SunOS balmyday 5.10 s10_51 sun4u    03/18/2004

12:36:32   device        %busy   avque   r+w/s  blks/s  avwait  avserv

12:40:01   dad1             15     0.7      26     399    18.1    10.0
           dad1,a           15     0.7      26     398    18.1    10.0
           dad1,b            0     0.0       0       1     1.0     3.0
           dad1,c            0     0.0       0       0     0.0     0.0
           dad1,h            0     0.0       0       0     0.0     6.0
           fd0               0     0.0       0       0     0.0     0.0
           nfs1              0     0.0       0       0     0.0     0.0
           nfs2              1     0.0       1      12     0.0    13.2
           nfs3              0     0.0       0       2     0.0     1.9
           nfs4              0     0.0       0       0     0.0     7.0
           nfs5              0     0.0       0       0     0.0    57.1
           nfs6              1     0.0       6     125     4.3     3.2
           nfs7              0     0.0       0       0     0.0     6.0
           sd1               0     0.0       0       0     0.0     5.4
           ohci0,bu          0     0.0       0       0     0.0     0.0
           ohci0,ct          0     0.0       0       0     0.0     0.0
           ohci0,in          0     0.0       7       0     0.0     0.0
           ohci0,is          0     0.0       0       0     0.0     0.0
           ohci0,to          0     0.0       7       0     0.0     0.0

The following table describes the disk device activities that are reported by the -d option.

Field Name	Description
`device`	Name of the disk device that is being monitored.
`%busy`	Portion of time the device was busy servicing a transfer request.
`avque`	Average number of requests during the time the device was busy servicing a transfer request.
`r+w/s`	Number of read-and-write transfers to the device, per second.
`blks/s`	Number of 512-byte blocks that are transferred to the device, per second.
`avwait`	Average time, in milliseconds, that transfer requests wait idly in the queue. This time is measured only when the queue is occupied.
`avserv`	Average time, in milliseconds, for a transfer request to be completed by the device. For disks, this value includes seek times, rotational latency times, and data transfer times.

Note that queue lengths and wait times are measured when something is in the queue. If %busy is small, large queues and service times probably represent the periodic efforts by the system to ensure that altered blocks are promptly written to the disk.