Whenever a RAID5 array experiences a failure, the entire rest of the drives must read every single sector correctly to reconstruct the failed drive. And since RAID is a block level operation with no concept of the filesystem, no shortcuts can be taken in unused space.
So... if RAID is
not a backup, and your data
(all your data!) in a RAID array is
at risk due to the non-trivial possibility of a second failure during extended multi-terabyte restructuring, and it
takes less time to recover your data from a backup than to restructure an entire RAID system...
Can someone please tell me what conceivable reason there is to have a RAID array? I have a drawer full of backup disks, plus a second set of backup disks stored off-premises down the street at my neighbor's house.
Yes, I know, with a RAID you can continue working uninterrupted if a hard drive fails. But is there
anyone on this bbs that does that? Or do you immediately shut down and replace the missing disk and then wait nervously for half a day while the system rebuilds itself? Whose work is so time-critical that they can't take an hour off to copy over the data from a single backup disk?
Not mine, that's for sure. But... YMMV.
tanstaafl.
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