Adrian Irving-Beer wrote:
On Wed, Apr 25, 2007 at 01:22:17AM -0400, Peter Sjoberg wrote:
I'm currently running linux sw raid but considering go hardware for my
next system.
Hardware RAID *can* be good for speed (RAID-0), and is particularly
good for things that involve parity bits like RAID-5.
For just about anything else, software RAID is much more recommended
by just about anyone I talk to.
Even though RAID modes like RAID-1, RAID-5, etc. all theoretically
increase redundancy, when done in hardware, they introduce an
additional single point of failure -- the RAID card itself.
For whatever reason, hardware RAID cards tend to be much more prone to
failure than any other part of the computer system in question,
*including the hard drives themselves*. And when the controller goes,
generally your whole array does, too.
Software RAID-1 across multiple disk controllers is the best way to go
if you really want redundancy, either on raw disks or on top of
hardware or software RAID-0 arrays (RAID-10) -- and even then, RAID
does *not* eliminate the need for regular backups.
RAID and tape backups solve two different problems. RAID gives you
enhanced disk performance and/or failover protection, depending on the
RAID level. Tape backups give you a means of disaster recovery. I don't
know where people get the idea that one is a substitute for the other.
The "you may not be able to recover your RAID volume if your controller
dies" thing is not something I worry about. If I have my system and my
data properly backed up on tape I should be able to recover it on some
medium in the event of a RAID controller failure. Surely it's no worse
than a JBOD disk dying? In any event, I have been using hardware RAID,
both SCSI and SATA, for the past 6 years on 4 different servers and I've
never had a controller fail. I've lost about 10 hard drives in the same
time period. My web application does keyword indexing and searching on
about a million files, and that is very taxing on both the drives and
controllers.
The issue of software vs. hardware RAID is also an issue of performance,
how much failover protection and system availability you need, and how
much your time is worth. Almost all hardware RAID controllers support
hot spares and hot-swappable drives. Plus they're generally simpler to
set up and maintain.