Assessing disk performance with the sar command

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The sar command is a standard UNIX command used to gather statistical data about the system.

With its numerous options, the sar command provides queuing, paging, TTY, and many other statistics. The sar -d option generates real-time disk I/O statistics. 
# sar -d 3 3

AIX konark 3 4 0002506F4C00    08/26/99

12:09:50     device    %busy    avque    r+w/s   blks/s   avwait   avserv

12:09:53     hdisk0      1      0.0        0        5      0.0      0.0
             hdisk1      0      0.0        0        1      0.0      0.0
                cd0      0      0.0        0        0      0.0      0.0

12:09:56     hdisk0      0      0.0        0        0      0.0      0.0
             hdisk1      0      0.0        0        1      0.0      0.0
                cd0      0      0.0        0        0      0.0      0.0

12:09:59     hdisk0      1      0.0        1        4      0.0      0.0
             hdisk1      0      0.0        0        1      0.0      0.0
                cd0      0      0.0        0        0      0.0      0.0


Average      hdisk0      0      0.0        0        3      0.0      0.0
             hdisk1      0      0.0        0        1      0.0      0.0
                cd0      0      0.0        0        0      0.0      0.0

The fields listed by the sar -d command are as follows:

%busy
Portion of time device was busy servicing a transfer request. This is the same as the %tm_act column in the iostat command report.
avque
Average number of requests outstanding from the adapter to the device during that time. There may be additional I/O operations in the queue of the device driver. This number is a good indicator if an I/O bottleneck exists.
r+w/s
Number of read/write transfers from or to device. This is the same as tps in the iostat command report.
blks/s
Number of bytes transferred in 512-byte units
avwait
Average number of transactions waiting for service (queue length). Average time (in milliseconds) that transfer requests waited idly on queue for the device. This number is currently not reported and shows 0.0 by default.
avserv
Number of milliseconds per average seek. Average time (in milliseconds) to service each transfer request (includes seek, rotational latency, and data transfer times) for the device. This number is currently not reported and shows 0.0 by default.