On Thu, May 15, 2003 at 10:22:20AM -0400, Matt Hyclak wrote:
> On Thu, May 15, 2003 at 10:10:15AM -0400, Jon LaBadie enlightened us:
>
> > Implementing the ability to split a DLE across multiple tapes would
> > continue a trend away from a feature of amanda that attracted me;
> > the ability to recover a dump using standard, non-amanda tools.
> > The RAIT driver was the first salvo to degrade this feature.
> >
>
> I agree with the statement about RAIT, but if amanda were spreading chunks
> accross tapes, how would that lose the ability to restore with standard
> tools? All you need to do is dd the n chunks off the tape, concatenate them
> together, and you have a complete {dump,tar,etc.} archive waiting to go, no?
> I think that would be extremely useful, and not turn so many people away
> from such a great program....
And Brian Cuttler asked:
>
> Couldn't you still recover from amanda tapes if the data where
> written in 'chunksize' bits across more than a single tape ?
>
> I mean, keep the chunks in order so you can find them, append them
> together when writing the tape to limit the amount of reassembly
> work. How are chunks re-assembled by taper now ?
>
> Couldn't we recover with "# dd" and "# cat >>" or would reassemble
> need to be more complex than that ?
Its not so much that you "couldn't". More the effort involved, where
the required information would be kept, and would existing implementations
be affected.
I suspect that with judicious use of dd and cat, I could reassemble a
3 tape RAIT dump. Not sure I'd want to try.
With the current scheme I've even done an emergency recovery of some
files on a WinNT system that had some ported unix utilities.
Consider a situation where you have no amanda installation and no
amanda records, only a tape, working tape drive, and a unix system.
And you are under pressure to recover a file before the boss goes home ;)
I was thinking of things like:
- how to know/where to keep the chunk size
- how do you know the tape file continues on to the next tape
- how do you deal with the partial last chunk on the first tape
which is duplicated on the next tape
- how will the file header on the second tape be different from
a file header for the start of a dump, will that break anything
Nothing insurmountable, but nothing as simple as position the tape,
dd skiping one block, optionally uncompres, unarchive. And certainly
not as simple to describe or include in the file header.
--
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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