Orion, NetApp, and iops
- From: Henry Poras <henry@xxxxxxxxxxxxxxx>
- To: oracle-l@xxxxxxxxxxxxx
- Date: Mon, 03 May 2010 12:24:53 -0400
I was taking some preliminary Orion runs on a new system just handed off to us. Orion ran and all the lineshapes looked about right (iops increased linearly with load until saturation) and really pretty, but there is some stuff I can't explain.
I was running against one LUN (made up of 3 aggregates) comprised of 48 disks (15K). Each disk can provide ~180 iops so I was expecting saturation at ~8640 iops.
orion -write 0 -num_disks 100 -duration 120 -num_large 0 (100% read, all 8K reads, -num_disks is high enough to crank the load, increase duration to allow enough aio calls in flight)
So for 8K reads and 100% reads I got my iops to saturate at ~67,000 (instead of the expected 8640).
-Was it a bug in Orion? I looked at iostat and it was consistent with Orion. -Was it read cache on the NetApp? Maybe, but I saturated at a load of ~35-50 which is consistent with my number of disks. This implies to me that I am actually hitting the disks. -Could it be some funny read ahead algorithm? Maybe Orion thinks it is doing 8 i/o calls, but the NetApp is doing some read ahead so only one call is an actual PIO and the rest are from cache. How can I test this? Is this an anomaly of the experiment? How could I disable this to get a better feel for production (or maybe this would still happen in production?)
-Any other thoughts?I don't like numbers without a model within which to understand them and storage is a bit of a black box to me.
Thanks. Henry -- http://www.freelists.org/webpage/oracle-l