How Good RAID is in Protecting Us from Data Loss?

How Good RAID is in Protecting Us from Data Loss? 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.
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bert [Entry]

"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."

bert [Entry]

"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."