Re: Is tape spanning documented anywhere?

Paul Bijnens wrote:

On 2006-06-13 12:10, Toralf Lund wrote:
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 tosay that it is not correct to claim that Amanda now suppots tapespanning, if it can't span dumps across tapes written in separate runs.
Shouldn't it be able to delete the corresponding data from theholding disk file as tape-chunks are successfully written - so thatonly the remaining chunks would be flushed on the next run? Seemslike this should be easy enough to implement, especially if youinteract with holding disk chunks in a constructive manner. Is thereany reason why nobody has looked into this, except for lack of time?
... or maybe what's on the holding disk does not really matter and/oris a separate issue. I suppose the taper already knows how to find acertain tape-chunk within the holding disk data, so it's more amatter of being able to tell it to start writing from a certain chunk(different from 0) during flush. The flush operation would obviouslyhave to find the correct index somewhere in the database. Does it doa lookup at all today, or just blindly tape whatever is on theholding disk?
Taping one DLE is several "runs" opens a can of worms:  you have to
add a notion of "partial" succeeded.  Restoring then needs some tapes
and some holdingdisk files.  What if the holdingdisk crashes or
accidently rm the files before all of it is written to tape? etc.

This would be a bit of an issue, of course. I'm wondering if the wouldthe situation be that much different from the one we have today, though.Holding disk crash or file removal is always going to be a seriousproblem, of course. But if you have a partial tape dump of the data, youwill at least be able to recover some of it... Maybe it would be wise tokeep all data on the disk until all tape-chunks are fully written,though, and also use the "partial" status only for flush purposes, i.e.consider "partial" writes as "unsuccessful" when doing restore etc.

What happens in the current version if amdump is interrupted whilewriting the 2nd tape, by the way?


As Stefan used to say:  AAPW(*).

Well, yes. I was partly also asking if a P would be W in this case,though, or if someone for some good reason had decided that tape splitacross runs should not be supported.


- Toralf