2009-08-31 05:50 AM
2009-09-01 07:50 AM
So...I'm not sure if this totally applies but I found at a previous site (where I worked for quite a few years actually) that AIX in particular had very different performance characteristics when given (1) LUN vs. (10) LUNs and a single filesystem on top (where the total space was the same and all LUNs were in the same volume actually).
This happened both with FC & iSCSI connectivity -- it basically seemed like inside AIX there was a max throughput (or maybe requests) per LUN. Making one filesystem across all those LUNs (no higher failure possibility to be honest since all the LUNs come from the same volume/aggregate).
2009-09-01 12:27 PM
Some bells were ringing before, but I got it now in detail!
It is probably due to IO queue length per LUN which is defined by HBA:
Emulex - 30 default per LUN (max of 128)
Qlogic - 32 default per LUN (max of 128)
These can be changed via HBA utilities, so I guess a single LUN with say 60 IOs queue length should give roughly the same results as a couple of them with 30 queue length each.