IO read/write size..maxphys

From: Beck, Joseph (jbeck@seic.com)
Date: Thu May 03 2007 - 14:24:48 EDT


Question:

What are the valid values for maxphys? Also, looking for
validation/sanity check of logic below, what am I missing.

Do I want the maxphys value to match stripe size on our storage frame?

Trying to tune I/O on a Oracle server that's doing a lot of data mining.
All datafiles are cooked.

Current env/setting:

E2900 - 8-way with 64GB RAM

EMC SAN, I'm told the stripe size for the hypers/LUNs is just under 1MB

maxphys: 131072

vol_maxio: 2048

stat cmds are showing::

iostat showing 128k read size

vxstat showing 989184

notes:

vol oradata02 1708409 416341 3301800182 11364730 63.5 2.9

3301800182 / 1708409

1932

1932 * 512

989184

So, the IO stack as I see it is:

Oracle (block size & multi-block read count) (8k & 16)

Vxfs (defaults)

Vxvm(defaults, vol_maxio: 2048)

OS (maxphys: 131072)

EMC (just under 1MB)

Joe Beck Ciber Inc. - a consultant to SEI One Freedom Valley Drive/ 100
Cider Mill Road| Oaks, PA 19456 | p: 610.676.2258 | jbeck@seic.com
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