[NCLUG] "Poor" RAID performance?

Sean Reifschneider jafo at tummy.com
Wed Mar 6 11:05:44 MST 2002


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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