Asynchronous IO stats

[randym]

How can I see what kind of usage my AIO servers are getting? The manual says to check the cpu % but they do not say what command to use. 'Smit aio' appears to only let you configure them but not see their usage. Any ideas?

 

[aixqueen]

http://techsupport.services.ibm.com...mode=9&documents=091401108611004&database=aix

How do I know if I need to use AIO?

Using the vmstat command with an interval and count value, you can determine
if the CPU is idle waiting for disk I/O. The wa column details the percentage of
time the CPU was idle with pending local disk I/O.

If there is at least one outstanding I/O to a local disk when the wait process
is running, the time is classified as waiting for I/O. Unless asynchronous
I/O is being used by the process, an I/O request to disk causes the calling
process to block (or sleep) until the request has been completed. Once a
process's I/O request completes, it is placed on the run queue.

A wa value consistently over 25 percent may indicate that the disk
subsystem is not balanced properly, or it may
be the result of a disk-intensive workload.

NOTE: AIO will not relieve an overly busy disk drive. Using the iostat
command with an interval and count value,
you can determine if any disks are overly busy. Monitor
the %tm_act column for each disk drive on the
system. On some systems, a %tm_act of 35.0 or higher
for one disk can cause noticeably slower
performance. The relief for this case could be to move data from
more busy to less busy disks, but simply having
AIO will not relieve an overly busy disk problem.

Important for SMP

For SMP systems, the us, sy, id and wa columns are only
averages over all processors. But keep in
mind that the I/O wait statistic per processor is not really a
processor-specific statistic; it is a global statistic. An
I/O wait is distinguished from idle time only by the state of a
pending I/O. If there is any pending disk I/O, and the
processor is not busy, then it is an I/O wait time. Disk I/O
is not tracked by processors, so when there is any I/O
wait, all processors get charged (assuming they are all equally idle).