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

01:00:00   fd0               0     0.0       0       0     0.0     0.0

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

Table 24–10 Output From the sar -d Command


Field Name	Description
`device`	Name of the disk device that is being monitored
`%busy`	Percentage of time the device spent servicing a transfer request
`avque`	The sum of the average wait time plus the average service time
`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 (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, rotational latency, and data transfer times)

Note that queue lengths and wait times are measured when there is something 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.

Examples—Checking Disk Activity

This abbreviated example illustrates the sar -d output.

$ sar -d
SunOS venus 5.9 Generic sun4u    06/24/2001

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

01:00:00   fd0               0     0.0       0       0     0.0     0.0
           nfs1              0     0.0       0       0     0.0     0.0
           sd0               0     0.0       0       0     0.0    39.6
           sd0,a             0     0.0       0       0     0.0    39.6
           sd0,b             0     0.0       0       0     0.0     0.0
           sd0,c             0     0.0       0       0     0.0     0.0
           sd0,f             0     0.0       0       0     0.0     0.0
           sd0,g             0     0.0       0       0     0.0     0.0
           sd0,h             0     0.0       0       0     0.0     0.0
           sd6               0     0.0       0       0     0.0     0.0