[CentOS-virt] Slightly OT: FakeRaid or Software Raid

Grant McWilliams grantmasterflash at gmail.com
Thu Dec 3 01:08:51 UTC 2009

> Personally, I never touch raid5, but then, I'm on sata.   I do agree
> that there are benifits to hardware raid with battery backed cache if
> you do use raid5 (but I think raid5 is usually a mistake, unless it's
> all read only, in which case you are better off using main memory for
> cache.  you are trading away small write performance to get space;  with
> disk, space is cheap and performance is expensive, so personally, if
> I'm going to trade I will trade in the other direction.)
Interesting thoughts on raid5 although I doubt many would agree. I don't see
how the drive
type has ANYTHING to do with the RAID level. There are different RAID levels
for different situations
I guess but a RAID 10  (or 0+1) will never reach the write or read
a RAID-5. The disk space waste
isn't too much of a problem anymore because as you say drives are getting
much cheaper. Although on that subject
I'll mention that enterprise drives and desktop drives are NOT the same
thing. We deal in hundreds of drives and see
about a 3% failure on desktop drives and only a fraction of that on
enterprise drives.

I will say though that in my opinion the one really important thing to
consider is the price. These controllers
aren't cheap and if you skimp you will pay. For sequential single reads
(streaming one stream) I'd consider
using a software "RAID" 0. For a mirror I'd consider Software RAID but once
I get serious and go for RAID5 or RAID6 I'd
only use Hardware RAID.

That's my 2 cents. :-)

Grant McWilliams
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