Re: Soft-RAID and Hard-RAID?

• Subject: Re: Soft-RAID and Hard-RAID?
• From: Kok-Yong Tan <email@hidden>
• Date: Tue, 30 Apr 2002 01:36:20 -0400

On 04/29/2002 17:16, "Kok-Yong Tan" <email@hidden> wrote:

While a RAID 5 config may function perfectly well with one drive
missing, what do you think will happen if you do so and another drive
fails before the RAID system is rebuilt? Unlikely, you say? Well,
it happened to me and, boy, will I not do it again!!! Now, I always
work on the worst case scenario, especially when handling data and
leave the "cowboying" to other people. Perhaps you've had bad
experiences with badly implemented RAID 1 solutions but the systems I
manage have complete failover where someone can yank a RAID-1 drive
out and it will failover instantly to the mirrored volume with nary a
hiccup. Of course, all our arguments are moot because they aren't
available to MacOS X Server. Oh well. Let's leave it at that.

The rebuild time depends on the implementation of the RAID. I've run 600GB
to TB+ raids, and the rebuild time for any one drive was measured in
seconds. More expensive? Sure, but if you need reliability, that's a price
worth paying. As well, what makes RAID 1 invulnerable to multiple drive
failures? You lose both dives of a mirror, and you're just as dead. RAID is
not a substitute for a good backup plan.

That's important, so let's make it more clear:

RAID IS NOT A SUBSTITUE FOR A GOOD BACKUP PLAN

It gives you more reliability, and allows you to have redundancy. But any
RAID can fail. I've seen systems with monster caches have one active, and
two hot spares die...all from a bad lot.

But to say that RAID 5 is more or less reliable than RAID 1 is simply
incorrect in the extreme. They are different ways to get the same thing
done. Both are fine in the even of a single drive loss. Both are uite dead
if multiple drives are lost before you can rebuild.

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