On 2006-06-13 10:32, Toralf Lund wrote:

  2. What happens to the holding disk file after a dump is partially
     written to tape? Will Amanda keep the entire file, or just what
     will be written next time around? And what if the holding disk
     data is split into "chunks"?

Amanda keeps the entire dump, and will be flushed entirely again
on the next amflush or autoflush.

You mean entirely as in the whole DLE? That would mean that tape splitting is restricted to multiple tapes written in the same run, which would be rather disappointing.

Yes indeed.  The whole DLE.  A singe DLE still needs to be written
in one run, possibly using many tapes.

But you may still split a veeeerrrryyyy large DLE into smaller ones
using the include/exclude mechanism that exists for a long time.
Only now you are not limited by the capacity of a single tape anymore.

Or maybe you misunderstood the question. Sorry if I was a bit unclear, but I'm not sure what terminology to use, now. What do you (should we) call one piece of output from the "tape split"? And what should "dump" be taken to mean? The entire output from the backup of one DLE, or one entry from the tape splitting. And what will a holding disk file contain, anyway? Again, will it be data for the whole DLE, or one instance of output from the split operation? (Like I said, I'm testing a bit as I write this, but haven't been able to draw any conclusions yet, mainly because I had to re-build amanda just now...)

A piece of a DLE on tape:  a tape-chunk.
A dump:  the entire output of dump/gnutar for one DLE.

One dump may be split in chunks on the holdingdisk.
One dump may be split in chunks on a tape.
These two chunking mechanisms are completely independent.

Note also that when you bypass the holdingdisk and do want tape-chunking
there is an addional parameter "split_diskbuffer" which gives the path
of a file Amanda can use to buffer one tape-chunk on disk (to be able
to feed the tape as fast as possible).  And there is even a third

But even when the last byte of single DLE did not make it to tape,
the complete DLE is considered failed (still on holdingdisk, or will
be tried again on the same level the next run).

Anyhow, when I said "holding disk file" earlier, what I meant was "the holding disk data for one DLE", and when I said "partially written to tape", what I meant was "some, but not all, split sections completely written to tape" (i.e. I was not talking about sections that are incomplete because end-of-tape is reached.)

I think I completely understood the question.  I had the same
terminology in my mind.

To confirm:  suppose you have one DLE:

Total DLE size (after compression):   295 Gbyte.
tape_splitsize 10 G
tape-capacity 101 G
runtapes 3
holdingdisk chunksize 2 G

And you also have some smaller dumps from other DLE's resulting in 20
Gbyte, which happen to be taped first.

The large DLE will will be spread over about 148 holdingdisk
chunks of 2 Gbyte each.

The first tape contains all those smaller ones already occupying
about 20 Gbyte, followed by 8 tape-chunks of the large DLE.
While writing chunk number 9, amanda bumps into eot, and restarts
that chunk all over again on the second tape.
The second tape contains 10 tapechunks more, nr 9-18.
While writing chunk 19 Amanda bumps into EOT again.
That 19th chunk is ignored on tape 2 and restarted again on tape 3.
Tape 3 contains tapechunks 9-28.

ANd while writing chunk 29 it bumps into EOT again.  But this was
the last tape we could use.  So the entire DLE, all the 295 GByte
is considered failed-to-tape.
All the 148 holdingdisk chunks are kept on disk.


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Paul Bijnens, xplanation Technology Services        Tel  +32 16 397.511
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