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I tried RAID before, because the idea that two hard disks mirror to each other, and thus prevent data loss in the event of bad sectors is appealing. But I discovered that once a hard disk went off, another would also go off, rendering the RAID useless.

How useful RAID is, in preventing data loss?

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up vote 1 down vote accepted

But I discovered that once a hard disk went off, another would also go off, rendering the RAID useless.

this is only valid for striped or spanned volumes. mirrored volumes are a different ballgame.

the various RAID levels are explained here.

and of course, RAID 1 is just another safety layer, not a substitute for a decent backup startegy.

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It is good, but should not be your only strategy.

Just remember,

RAID is not backup!

As Kevin Dente wrote on Serverfault -

RAID guards against one kind of hardware failure. There's lots of failure modes that it doesn't guard against.

  • File corruption
  • Human error (deleting files by mistake)
  • Catastrophic damage (someone dumps water onto the server)
  • Virus'
  • Software bugs that wipe out data ..
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...and of course, you can have another drive fail right after the first one (or, during the rebuild). I had a RAID 5 array of 4 drives lose a second drive while we were swapping in the replacement for the first failed drive. – Brian Knoblauch Sep 24 '09 at 11:25

RAID should be used to provide availability of data, it should not be thought of as a way of keeping it safe. Keep off-site backups of anything crucial. If a drive dies, then the server can continue to run if RAID is properly configured and the users will not be interrupted. If you have a fire break out then all the RAID in the world won't protect your data.

As for the RAID breaking if a drive dies - Either you have mistakenly configured RAID 0, which provides no redundancy at all. Or you have somehow misconfigured something.

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