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Old 10-24-2008, 10:36 AM  
Phil21
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Join Date: May 2001
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Doesn't sound like you ran into the problem described in the article.

The "mathematical certainty of a read failure during rebuild" has been well known for some time. This is why nearly every modern RAID controller supports RAID6

You'll see it during an actual rebuild, say halfway through, where a *second* disk will throw offline, thus trashing the array completely.

Also, background consistency checks do not help in this scenario. The read failure rate given in the article is for fully operational disks - e.g. it's completely normal for them to throw a bit here and there.

The article does go a bit overboard though. For one, very few arrays are going to be 100% maxed out on use, thus your chances for an error are substantially lower. We still utilize RAID5 for any 6 drives or less arrays, and have yet to have a dual disk failure as described (although, we've had two complete disk failures which are unrelated to the problem discussed).

All in all though, remember backups! RAID is in no way, whatsoever, not even close, a substitute for a proper backup strategy. If the server availability is extremely important, have a warm-spare handy that is sync'ed on a regular basis, as restores from backups can take quite some time depending on your content set.

-Phil
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