High %wio in sar output

[Stojcevski Dejan]

Hi to all,
On one server (rp4440/$GB RAM/2 CPU's x 800MHz with EVA 3000) I have a strange situation of extremly high numbers in %wio column in sar output. Now, we know what is the reason of this abnormality: we have an Informix IDS database with one HUGE table. Index of this table is very big - when we drop this index - the situation is going to normal. So my question is if we can solve the issue with some kernel parameter modification? OS is HP-UX 11i so some parameters can be changed "on the fly". I already tried with scsi_max_queue parameter but it did not give me the results. Informix is using the raw partitions - not file systems.
Attached is some sar outputs from the system.
Thanks in advance.

[Jaime Bolanos Rojas.]

Stojcevski,

The most difficult part of the performance issue, sometimes is to find the root cause of the problem.

If %wio is high, it could be an indication of a disk bottleneck
or it could be ( most likely ) that the CPU has nothing else to do while it
waits for a process to complete its I/O's.

Most of the performance problems are fixed are the database level, but tuning them right, a huge Index will usually do the trick.

There is no much that can be done at the OS that will better your performance if that DB is not tuned.

Regards,

Jaime.

[Steven E. Protter]

Shalom,

Yesterday I had slow response on an EVA-4000. HP updated the firmware to most current and the problem went away completely.

Also note LUN configuration is an issue. If a LUN is to have heavy write access it should be configured RAID 1. This uses twice the space but writes are much quicker than Raid 5.

I've never solved a problem like this with kernel parameters.

SEP