RAID questions (was Re: [TriLUG] Re: Dieing hard drive?)
mike at enoch.org
Tue Nov 30 21:54:52 EST 2004
Aaron S. Joyner wrote:
> IMHYAO, Raid 5 is only a good choice if you are using a large number of
> drives, and can incorporate a hot spare or two - or if you really can't
> afford to sacrifice 50% of the capacity of the purchased drives.
For home fileserver use, RAID 5 should be fine. RAID 5 suffers when
performance is needed. For a home fileserver, that may not be an issue.
We're not talking about editing large video files, so RAID 5 is
likely to be perfectly adequate. Of course, it depends on how much
storage space you're looking for. If 160GB is enough, then two 160GB
drives and RAID 1 would be great. If you want 320GB, then three 160GB
drives in RAID 5 would be great. If RAID 5 isn't fast enough, increase
the filesystem cache size and move on. RAID 5 reads aren't as bad as
RAID 5 writes.
> I'd generally suggest the controller. The advantage being that it gives
> you another set of IDE channels to attach those drives to (as you may
> need them since they is not going to be your only disks). It also
> pretty-much ensures that you're going to have hot-swappable channels,
> which is a nice feature in a RAID setup, given that one of the main
> purposes of RAID is to keep things up and running should a disk die.
> Another consideration in the RAID 5 vs mirroring debate is that most
> cheap RAID cards can't do RAID 5, and it is a larger software hit to do
> the checksumming and other processing on the host system.
The biggest gotchya with RAID cards that many people seem to overlook is
that the on disk format of the actual bytes is specific to that
controller. If your controller dies (it happens!), you -must- replace
it with an exact duplicate card, or you will not get your data back.
And there's nothing stopping a vendor from releasing a new version of
the card that uses a different chip without saying so on the box. If
you go the hardware route, buy two of the cards, right off.
If you go the software route, then a controller failure is no big deal.
You simply move the drives to a different system and you're golden.
Plus, don't most of us have a lot of spare CPU time on our fileservers?
More information about the TriLUG