On Wed, Sep 26, 2007 at 04:26:50PM -0400, Jean-Francois Malouin wrote:
>
> One of the most important feature of amanda was (it still is but read
> on) the possibility of doing a bare-metal restore with just a few
> utilities. I say was because in my case the ever increasing amount of
> data, the size of the DLEs and the number of chunks needed in order to
> fit in my tapes (LTO-1 and LTO-3) was getting out of hand --too much
> likely to 'forget' some data while including/excluding dirs in a DLE--
> so I had to use the tape spanning feature. I get a much better tape
> usage but now I can't do bare-metal restores in case something real
> bad happens. I understand that I can't have both the cake AND the
> cherry but I would be hard pressed to justify using amanda to our
> computer people at my site when such an important feature is missing.
>
Jean-Francois,
I think you lose less than you realize. I've not tested a bare-metal
restore with my spanned dumps, but here is how I view the procedural
difference from a non-spanned dump.
For non-spanned:
1. you need to locate the specific tape file where the DLE begins.
2. you need to use mt to position your tape at the beginning of the file
3. you need to use dd to strip off the first 32KB of the tape file.
4. you need to feed the rest of the file to your restore command(s),
eg. unzip, tar, ...
For spanned:
1. the same except you also need to determine the number of chunks and
whether it spreads to multiple tapes
2. the same
3. a modification
4. the same
Recognize that the spanned pieces are all one after the other on the
tape, and if crossing to another tape, at the beginning of that tape.
But, if it crosses to another tape, the last chunk on the tape is
not valid.
So step 3 becomes not one "dd bs=32k skip=1 ..." but a loop through
the chunks doing the same dd command on each chunk. In a scenario
where you knew the dump was in 5 chunks, step 3, piped into step 4
could be simply:
for i in 1 2 3 4 5
do
dd bs=32k skip=1 if={your tape dev}
done | {step 4 commands}
Obviously it would be more complex if the DLE were split over
multiple tapes, but then something like this is possible:
(
FOR LOOP FROM ABOVE
tape change commands
tape position commands (to skip over amanda tape header to first file)
ANOTHER FOR LOOP
) | {step 4 commands}
And I've ignored the bad last chunk.
If sufficient disk space were available, you could just save
each chunk with a sequential number. Then cat the chunks
piping them into the step 4 commands.
Amfetchdump tries to automate this.
And if I understand the -i option, assists in locating the chunks.
But it still can all be done manually.
What you lose by spanning is the simplicity of having the entire
dump in a single tape file. But the manual recovery procedure
is still basically the same.
--
Jon H. LaBadie jon AT jgcomp DOT com
JG Computing
4455 Province Line Road (609) 252-0159
Princeton, NJ 08540-4322 (609) 683-7220 (fax)
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