Re: RAID 1 versus RAID 5

From: Joshua Bolton (JoshuaBolton_at_discussions.microsoft.com)
Date: 12/03/04 

Date: Thu, 2 Dec 2004 16:59:07 -0800

actually raid 5 has a minimum of three drives. It can have many more drives
than three. More drives in raid5 the more you can have fail without losing
everything.

You should give serious consideration to configuring hot spares in your raid
array. These hot spares allow the raid card to rebuild the array on the fly
when a disk dies. Not only does this save you having a slow network when
your 3disk raid array is running on two drives but can also prevent losing
everything.

Here's the reason why. Usually when you get a lot of drives they are from
the same manufacturer and the same lot. This also means they are going to
have the same mean time before failure [mtbf] rating. So the odds are if you
lost one drive you could at any time lose a 2nd drive. I have had exactly
that happen. Before I could replace the failed drive I lost a 2nd one.

This is why I don't use raid5 anymore [use raid 0+1 and 10] and always
configure 2 hot spares minumum in the system. I also buy drives from
different sources [same drives] in an attempt to get different lots.

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