isolating catalogs for robust data protection

Hello,

I was disappointed to read that someone on the support list was not
able to recover his data because he lost his last slice.  I wasn't
disappointed because he couldn't restore his data, although I feel for
him - been there, done that - but because in response he was told it
would not have mattered if he had an extra copy of the isolated
catalog.  This seems to take away greatly one of the benefits of using
dar:  one corrupt section of data does not ruin the whole archive.

I have just started using dar and one thing I was expecting to be able
to do was put a copy of the catalog with each slice onto DVD.  So in
the event that the last DVD should get destroyed or even just
scratched in the wrong place, I could restore the majority of my
backup.

The -A option is already there!  dar -x archive -A catalog.

Now, like I said, I'm new to this, but if he would have added that
catalog to dar_manager,
would he still need the last slice?  But is this a solution or a mere
side-effect?

I'm _not_ suggesting that a catalog _should_ be maintained with each slice.
I'm asking that -A lets me use an isolated catalog to restore from any
given slice.  Then I can choose whether or not I want to isolate the
catalog and make copies.

We still have one more problem:  the first slice.  dar requires the
first slice.  But why do we really need the first slice?  We don't
need it for decompression.  We don't need it for decryption.  We don't
need it to find out if we're dealing with slices or not.  We need the
first slice only to find out four little bits of information -
version, compression algorithm, command line, and if EA was saved. 
So, if the first slice were to be corrupted or the archive header
mangled in some way, we then have the same problem with the whole
archive becoming useless.  Replicating the archive header on each
slice would make a negligible impact on file size while greatly making
the archive more robust.

With these features,  I could use the first disc to do a full restore
without having to insert discs _three_times_.   More importantly, I
could restore any random, surviving slice without changing discs at
all.

Comments?

Thank you,
--
Robert Dale


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