[NCLUG] Re: [lug] "Poor" RAID performance?

Sean Reifschneider jafo at tummy.com
Wed Mar 6 13:39:26 MST 2002


On Wed, Mar 06, 2002 at 11:40:57AM -0700, Riggs, Rob wrote:
>You probably need to tune your RAID configuration. Even Adaptec's
>comparisons of the Mylex with their 3210S controller show the Mylex

It's set up with 64KB stripe size, which seems about right...  I built the
file-system that the tests were run on to match this.  The drives are (for
some unknown reason) configured all on the same channel.  Considering that
I'm seeing peak performance roughly 20% of the bus capacity, I don't really
believe that is contributing...

>performing significantly better than what you are seeing.

Under NT...  Perhaps it's an issue with the DAC960 driver on Linux?

>Are your disks spread across both channels? How much cache is on the
>controller? How big are the stripes? 

No (don't ask :-/), 32MB, and 64KB.  With the exception of not having the
drives on both channels, this is the same configuration that they were
using on the Adaptec tests.  We have 2 less drives, and they didn't say
what the test drives were (only that there were 8 of them).

I guess I was underestimating the hit that RAID-5 can have on writes, but
I'd expect with a butt-load of sequential writes that the controller would
be caching the data and not having to read from 4, update 2.  I'd expect it
to have enough data that it would be updating 6 all the time.

Sean
-- 
 The only people who have anything to fear from free software
 are those whose products are worth even less.  -- David Emery
Sean Reifschneider, Inimitably Superfluous <jafo at tummy.com>
tummy.com - Linux Consulting since 1995. Qmail, KRUD, Firewalls, Python



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