On Sunday 07 September 2008 03:04:21 Michael Heim wrote:
> Hi Kern,
>
> can't you use something like data spooling for this?
>
> First step: Make a virtFull to a temp spool file on disk
> Second step: Spool this to the destination
Yes, interesting idea. It could possibly help in some cases, but the problem
is that it doesn't scale well enough. Take for example an extreme example:
someone has a backup to tape amounting to 10TB. With this, suggestion, it
would be necessary to spool 10TB to disk then to write it to tape. Someone
with this size of data will require a solution that is tape to tape ...
I think the best suggestion so far has been to add new code in Bacula that
uses the volume list (list of volumes to be read) to ensure that none of
those volumes are selected for writting. That will provide a quite
reasonable means of ensuring there are no deadlocks -- providing the user has
two drives available.
Best regards,
Kern
>
> regards
> Michael
>
> Kern Sibbald wrote:
> > Hello,
> >
> > As many of you know Virtual Backup (consolidation, synthetic full, ...)
> > is a new feature that is implemented in the development trunk and
> > scheduled to be released later this year. It essentially copies what
> > would be a "full current" restore to a new Volume thus creating an
> > virtual backup that can serve as a Full backup. This has a lot of
> > advantages, particularly for sites with full backups that run long times
> > or for remote sites where the time to transmit a full backup is
> > excessive.
> >
> > The Virtual Backup feature works much like Migration and Copy. It reads
> > from the required Volumes and writes to a Volume specified in the pool as
> > "Next Pool". This ensures that the read and write Volumes are different.
> >
> > Everything seems to work fine with the Virtual Backup. However, thinking
> > about longer term operations, it has occurred to me that when you want to
> > make a second Virtual Backup things will become very complicated. First,
> > the Virtual backup will want to read the previous Virtual backup volume,
> > and then if that Volume is not full, it will want to write to the same
> > Volume. Even if the volume is full, you will be in a situation where the
> > Job will want to read and write to volumes in the same pool. In all
> > those cases, there is no guarantee that there will not be a deadlock
> > situation (actually Bacula currently cancels any job attempting to read
> > and write from the same Storage device).
> >
> > I am not 100% sure what to do to resolve this issue. I suppose one could
> > run a Migration job to "move" the Virtual Backup back to the Pool from
> > which it originally came, then the next Virtual Backup would work fine
> > (the same as the first one), but that sounds a bit kludgie.
> >
> > If anyone has any suggestions, I would appreciate to hear them. However,
> > suggestions that require implementing significant amounts of code or
> > complex new algorithms such as deadlock detection won't be very helpful
> > since there is no time left to do such implementations between now and
> > release time. In addition, deadlock detection won't help, what we really
> > need is deadlock resolution, and that is an even more difficult subject.
> >
> > Best regards,
> >
> > Kern
> >
> >
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