[CentOS] Calling All FS Fanatics

Feizhou feizhou at graffiti.net
Thu Oct 5 04:12:39 UTC 2006

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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