Les Mikesell wrote:
On Wed, 2006-10-04 at 11:29 -0400, Joshua Baker-LePain wrote:
Does anyone have any bonnie++ results for Linux software RAID 5? I know
software RAID 5 does not really lend itself to a performant software
implementation, but the results would be interesting to see, none the
less.
Actually, md is a *very* good performer (although I don't have any
benchmarks on hand at the moment). The reason I stick with hardware RAID
is that md doesn't handle hot swapping all that well. Not taking systems
down to replace bad disks is a Good Thing.
Now that disks are not so expensive you have to look at the difference
in performance with raid 5 vs. raid 1 or 0+1. Raid5 essential ties
all of the disk heads together and seek time is usually the bottleneck
unless you have a single process accessing a huge file. Of course these
days you can also throw RAM at the problem and at least avoid the seek
to read the block that you are going to partially overwrite by having it
already in the buffers.
raid 1+0 will trounce raid 5 in most situations. Been there and done
that. The only area where raid 5 really makes absolute sense is large
archives that are rarely modified and not constantly written to. Given
enough disks, very little should be able to match raid5 read
performance...until one disk goes down...then the bottleneck becomes the
processing power available so software raid 5 will likely trump raid 5
on hardware raid cards.
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