[nSLUG] raid performance

Rory rory at unixism.org
Thu Jun 22 22:54:47 ADT 2006


I know some folks on this list have experience building heavy lifting
Linux boxen so here's a quandary:

Having recently switched to 2.6.15 kernel we are finding that the RAID
performance completely sucks.  Specifically RAID 10, on Dell 2850 with a
Perc4 controller.  This is an LSI based controller and therefore uses
the megaraid driver.  This is initially perplexing given that with the
new I/O schedulers in 2.6 things should improve.  We've tried all the
schedulers including the no-op one with no appreciable change in crappy
performance.

By crappy performance I mean reads are an order of magnitude slower than
with 2.4 and writes even slower.

The part that is really burning our collective noodles is that very
similar performance problems exist when using software raid with 2.6. 
Reverting back to the 2.4 kernel on the same hardware returns
performance to previous both with megaraid and software raid.

I'm not the one working directly on the problem but since I've been
asked for my opinions I thought it would be worthwhile to check here and
see if this rings a bell for anyone before I dive deep into kernel
debugging mode.

R


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