Re: backup archive format saved to disk
Ron Johnson wrote:
RAID is *not* for archives!!!
RAID was not designed for archives. I can see no reason why
it wouldn't work for that. RAID 1, for example, is simply
making two (or more) copies of the data. Are you saying that
making more than one copy of a backup is not a reasonable
approach?
I see no reason why RAID 5 could not be used when data
span multiple CDROMs, for example. Let's consider the
case where the data span two CDROMs, and one wants
some assurance that if one of the media fails, the
data will still be recoverable. Then one can write the
two CDROMs, and then write another which is the bitwise
XOR of the other two CDROMs. If any one of them fails,
all data are recoverable. This only takes 1.5x as many
discs, whereas making two copies would take 2x.
Essentially, with RAID 5, one uses some version of a
systematic BCH code with the check bits stored across
the additional drives. Then, if one or more of the drives
should fail, the data on the others could be used to
reconstruct the data. I see no reason why this could not
be applied to CDROMs, or any other archive medium.
The main advantages would be that one would essentially
have burst error correction of the size of the disc
(this being, with the FEC on the disc, if any, an
interleaved code in effect), which is enormous, indeed,
and economy in storage over using multiple copies, as
illustrated above.
Mike
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