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

[Riggs, Rob]

You probably need to tune your RAID configuration. Even Adaptec's
comparisons of the Mylex with their 3210S controller show the Mylex
performing significantly better than what you are seeing.

http://www.google.com/search?q=cache:fQY5PNjvfcsC:www.adaptec.com/go/3210S_b
enchmark/+Mylex+AcceleRAID+352+&hl=en

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

Make sure the disks are split across both channels and play with the stripe
size.


-Rob

-----Original Message-----
From: Sean Reifschneider [mailto:jafo at tummy.com]
Sent: Wednesday, March 06, 2002 11:06 AM
To: lug at lug.boulder.co.us; nclug at nclug.org
Subject: [lug] "Poor" RAID performance?


I was recently running some performance tests (bonnie++) on a RAID array
and was fairly suprised at the performance, or lack thereof...  Since Rob
in the past has mentioned that current SCSI discs can saturate 80MB/sec
controllers, I'd assume that he's seeing something in that neighborhood.

The setup is a Mylex AcceleRAID 352 dual channel U160 controller, with 6
10KRPM drives set up in a RAID-5 array.  According to the controller, all
drives are talking to the controller at 160MB/sec.

So, what is this "poor" performance?

            ------Sequential Output------ --Sequential Input- --Random-
            -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
       Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
      8000M  7089  56  7196  11  5969   5 12242  97 32905  21 381.1   3

Am I just expecting too much from a mid-end RAID setup?  These numbers are
not all that much better (and are in some cases lower) than my laptop's
single 4500RPM IDE drive.

            -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
       Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
       700M  5508  82 15684  17  6775   5  4918  77 12615   5  90.4   0

For comparison sake, I've also run bonnie against 3 7200RPM IDE drives in a
RAID-0 array (though these drives were kind of mixed and matched, some at
least a year or two old -- not running the high bit densities seen
currently):

            -Per Chr- --Block--  -Rewrite-   -Per Chr- --Block--  --Seeks--
       Size  K/sec %CP K/sec %CP  K/sec %CP  K/sec %CP  K/sec %CP  /sec %CP
       2000  8616 78.3 49499 56.7 29567 35.2 10695 94.9 66362 36.1 237.5 2.1

Am I just wrong to be expecting a $3k RAID array to be faster than, say, a
laptop IDE drive?

Sean
-- 
 "The big bad wolf, he learned the rule.  You gotta get hot to play real
cool."
Sean Reifschneider, Inimitably Superfluous <jafo at tummy.com>
tummy.com - Linux Consulting since 1995. Qmail, KRUD, Firewalls, Python
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