Raid 5 (was: Mounting of Linux volumes)

Corey Edwards tensai at zmonkey.org
Thu Dec 1 20:40:24 MST 2005


On Thu, 2005-12-01 at 18:08 -0700, Ross Werner wrote:
> 1) Which RAID level do you use, and in hardware or software?

RAID 5 in hardware. RAID 1 in software and hardware.

> 2) Why do you use RAID?
>    a) In case a drive fails
>    b) Performance benefits
>    c) Mistaken idea that RAID is the same as doing backups
>    d) Other?

We use RAID (especially RAID 1) to protect against drives going belly
up. Somebody else mentioned a 1/1000 chance of a drive dying on any
given day, and I would say that's pretty accurate. Or more often.
Hardware RAID is tops since you can swap in a new drive with no
downtime. Software RAID is OK for systems that can sustain short periods
of downtime, such as our outbound mail cluster which has multiple
machines in it.

> 3) If you use RAID 5, what's the biggest reason you'd use it over RAID 1?

I'm starting to believe less and less in RAID 5. Sure it's a nice way to
make a big volume, but the more disks you add the more likely you are to
have more than one fail. If that happens, you're toast.

Now with RAID 10 you lose capacity vs the same disks in a RAID 5, but as
you add more disks the chance that two drives in the same RAID 1 pair go
out actually goes down. And in the performance category, you've got more
spindles.

Corey

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