Raid 5 performance

[Lennart Sorensen]

On Tue, Sep 21, 2004 at 03:01:17PM -0400, Martin Duclos wrote:
> I've decided to install a raid 5 on a file server at home. CPU is pentium 
> 120MHz with 64M ram. I know it's rather scarce but my question is, is there 
> a way to measure where the biggest performance hit will be? I want to know 
> of a way I can monitor which compenent is the bottleneck. Will increasing 
> memory improve performance? Will faster CPU make a difference? I'm looking 
> for a real technique (ie numbers) from which I can get a better 
> understanding. I've looked at google groups and all I can really find are 
> opinions and vague references to "if you have this or that it might give 
> you better..."

Hardware or software raid?  raid5 is one of the processing heavy (mainly
xor) raid implementations, so you will have some performance impact if
you run software raid.  The software raid code in the kernel does have
mmx and sse code paths to speed up the calculations onf machines which
have those instruction sets, which a P120 of course does not.

Adding ram shouldn't make any difference to the raid, while a faster CPU
would make a difference if using software raid.

With hardware raid the card does the xor calculations and hence the cpu
speed isn't really relevant.  It is possible in some cases on high end
machines that using software raid will run faster than hardware raid
since the main cpu is many times faster than the dedicated cpu on some
hardware of the cheaper raid cards.

How many ide ports do you have or are you planning to use scsi?

Lennart Sorensen
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