Re: Is tape spanning documented anywhere?

Paul Bijnens wrote:

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 tapesplitting 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.

Oh no... Like I said, that's a big disappointment. I'm tempted to saythat it is not correct to claim that Amanda now suppots tape spanning,if it can't span dumps across tapes written in separate runs.

Shouldn't it be able to delete the corresponding data from the holdingdisk file as tape-chunks are successfully written - so that only theremaining chunks would be flushed on the next run? Seems like thisshould be easy enough to implement, especially if you interact withholding disk chunks in a constructive manner. Is there any reason whynobody has looked into this, except for lack of time?


But you may still split a veeeerrrryyyy large DLE into smaller ones
using the include/exclude mechanism that exists for a long time.

Yeah, I know, but hasn't the fact that you have to do that always beenseen as the one big limitation of Amanda? I was hoping this was gone nownow ;-(

This thing is, setting up the exclusions/inclusions right is nearlyalways non-trivial on a system with dynamic data, and in a setup I'mlooking at now, it will simply be impossible to specify a static configfor this. Without real tape overflow support, we'll simply have toupdate amanda.conf every day. The actual update may perhaps be doneautomatically, but I was rather hoping I wouldn't have to implement atool for that, and the dump database etc. will obviously also get verymessy.

Differently put, I don't want to set up an amanda config which has theodd DLE that's slightly larger than a tape - I want *all* DLEs to belike that. I may be able to assume that they are never larger than twotapes, so I could use "runtapes 2", but I fear that this would lead totoo much waste of tape space. I suspect the only way to get the fulldumps evenly split across a relatively limited number of tapes, will beto set "runtapes" large enough for all full dumps to fit into one run,but this is probably not possible in practice.

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 bitunclear, 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 whatshould "dump" be taken to mean? The entire output from the backup ofone DLE, or one entry from the tape splitting. And what will aholding disk file contain, anyway? Again, will it be data for thewhole DLE, or one instance of output from the split operation? (LikeI said, I'm testing a bit as I write this, but haven't been able todraw any conclusions yet, mainly because I had to re-build amandajust now...)
A piece of a DLE on tape:  a tape-chunk. [ And so on ]

OK. Thanks.

- Toralf