<quote who="David">
> I installed a hardware raid some time ago for backup/security. One of the
> disks became corrupted and the other dutifully mirrored the corruption.
> I'm not a geek, so I questioned the manufacturer of the raid card and they
> simply told me that raid copied whatever was there! Huh?
>
> Does anyone have any comment about this?
That's exactly what RAID is meant to do - if it doesn't, it's a very serious
bug! :-)
Backup is when you take data from a known time (you can't assume it's known
good data) and archive it; then you know you can fall back to a given
archive from a given date.
RAID is 'Redundant Array of Inexpensive Disks', used to protect against
immediate hardware failure. If one drive dies, the other is exactly the same
and can continue on (for a simple RAID-1 case anyway, the other levels work
differently but generally achieve the same ends). It's exactly the same data
because your software or hardware RAID implementation has been writing it to
both (or more) disks at every point.
RAID can help you with backups though; if you fail one of the disks off the
array (mimicking a hardware failure), you can back it up as a snapshot of
your data, without getting in the way of other processes. When you bring it
back online, the disks sync and everyone is happy again.
The above is mostly useful with RAID-1, but some systems can do a similar
thing with other redundant RAID levels, or volume management systems (such
as LVM in the Linux world). Pretty sweet.
- Jeff
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