Raid 5 performance

[Mike Kirk]

> 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 think you'll be CPU limited with software RAID 5 on that system. Actually
you don't really have enough memory for an effective file cache either: I
vote you just replace it like some of the other posters said :). I guess it
all depends on what you're using it for. It may not be fast, but it will be
reliable.

To get some number you could do something like  "bonnie++ -d
<filesystem> -x1 -u0 -f -q" ... it will dump out numbers for KB/s
read/write/rewrite on your array, plus give %CPU for each. I just played
with some hardware/software RAID5 myself and I found it could take up to
nearly 30% CPU on an AMD 2700+ with 8 drives. In my case the extra CPU was
essentially free anyways.. so I used software RAID.. effectively reducing a
pricely hardware RAID card to a 8-port IDE controller. The tables in this
Star/OpenOffice doc give an idea of what bonnie++ spits out:

http://battlemage2.dyndns.org:88/Hardware_vs_Software_RAID.sxc

As for others who say network IO is the limiting factor, well, an Intel GigE
card is about $75 or less these days: I think with networking getting this
cheap it's still the drives that slow things down.

Of course, being new to Linux, I could be talkin' outta my butt :) Hope your
setup works out OK!

Regards,

Mike




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