Originally posted by: SystemAdmin

Hi,

We have built a new lpar for migrating a Solaris based Oracle DB to AIX. During some of the prelimary testing performed by our DBA it was apparent that our AIO setting (default) were incorrect and caused the DB to crash. After some research in to AIO tuning I have some questions as to the terminology used.
The information following is the formula indicated for tuning AIO settings. This came from an AIX Oracle white paper concerning Oracle Tuning:
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minservers = 10 * # cpus

maxservers = (10 * # disks) / # cpus

maxreqs = a multiple of 4096 > 4 * #disks * queue_depth
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Questions:
1. # cpus? Do we use physical or logical cpus count for this variable?

2. # disks? Is this LUNs, spindles, hdisk, hdiskpower...? We assume to use only the disk associated with the data, not the app, redo or archives?

3. queue_depth? Where is this ascertained from?

Our current specs:

OS: AIX 5.3L; Oracle version:10g
7 dedicated CPUs
18 GB RAM
3 volume groups containing 36 luns (SAN presented of which I was told 192 spindles)

Any and all information is greatly apprieciated.

djn
#AIX-Forum

Originally posted by: MarkTaylor

10 * num cpus:- for minservers is actually fairly high, so I would use physical for that one to err on the side of caution.

number of disks:- as they have based this calculation on queue_depth, then I would summise that they are looking for logical disks (as you set the queue_depth on the logical disk)

queue_depth:- this tuning usually comes recommended by the disk manufacturer. Done a bit of digging and it looks like 16 or 32 are supported (default of 8) but you would need to contact EMC really.

HTH
Mark Taylor


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Originally posted by: SystemAdmin

There are one more thing you need to consider is maxrequests in AIO parameters. Which is most important parameter in AIO. By default max requests are 409 i think . You can increase that value to 12288. which was recommended by other application vender's.
#AIX-Forum

Originally posted by: SystemAdmin

You can also monitor the number of AIO servers with the option "A" of nmon to verify is the "All time peak" is near to your "maxreqs" parameter and then you can increase the maxreqs dinamically.

Asynchronous-I/O-Processes
Total AIO processes=1863 Actually in use= 4 CPU used= 1.4% [Use zero
All time peak=1863 Recent peak= 54 Peak= 48.2% to reset]

Regards,
Leo
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