Re: backup compress on the fly
Alvin Oga wrote:
On Mon, 3 Oct 2005, Mike McCarty wrote:
The point is that, if there is an error, all the CRCs in the
world won't put the data back together again. If one uses
crc or ecc ??
More correctly, FEC (Forward Error Correction).
Note that even FEC cannot repair everything.
most "large capacity" drives uses ECC which does support error correction
at least in the firmware and tape controllers to read the data
off the tape ..
So has every hard disc. But we still get disc errors, don't we?
OTOH, if the
whole image on tape is a compressed one, then tar or gunzip or whatever
is simply going to complain that the one (and only) file in
the compressed archive is corrupt and unrecoverable.
there's an asumption that you only have 1 compressed file
on the tape
If you read what I wrote carefully, you'll see that I stated that "if
the whole image on tape is a compressed one" as opposed to "if the
image on tape contains compressed files". In this particular thread,
the context specifically mentioned as a possibility using tar with
the "z" compression option specified, which results in a single tar
image which is then compressed, or possibly piping the output from
cpio into gzip.
whilest you can in fact have multiple files on the tape
Well, all I can say is that what I wrote was specifically
intended to point out what the circumstances in which my statement
would be true were. You seem to be trying to get me to
realize that they may not be universally true, when I already
tried to prevent getting that kind of response.
Perhaps in future I'll have to be more specific.
<flame bait>
tapes for backups is like to stoneage of the flintstone
</flame suit left on>
[snip]
Flame troll declined.
All techniques for achieving any given goal have relative
advantages and disadvantages. Not any one method is
universally better than all others in all circumstances.
Decisions about what to use for backup depend critically
upon information not present in the current thread.
Mike
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