[lug] "Poor" RAID performance?

[John Hernandez]

 From what I know about RAID, you can expect RAID5 writes to be 
expensive compared to a single disk write.  In the read department, you 
should expect good performance; for sequential reads and random seeks, 
if I read this correctly, you are getting about 3x the performance of 
your laptop drive.

Sean Reifschneider wrote:

> 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
> 


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