Kern Sibbald wrote:
On Monday 11 July 2005 18:50, Phil Stracchino wrote:
On Mon, Jul 11, 2005 at 11:44:36AM +0200, Ren? Brask S?rensen wrote:
Hi All
Don't know if this is the right list to ask.
I have been looking through the bacula documentation but couldn't find
anything about delta compression. Do backula support any kind of delta
compression ? or are there any plans for implementing it i future
releases ? I'm asking because it frustrates me that I every night
transfer one file that's over 1Gb. If I had a tool which supports delta
compression I could greatly reduce the amount of data transfered.
This is something that has been discussed in the past, but no-one has
yet worked on an implementation to my knowledge.
I haven't read about how rsync and zsync work, but I suspect that it is called
delta comparison rather than delta compression since the incremental backup
of only what changed is based on a rolling file signature or checksum rather
than a compression technique. In fact, compressing the files can create
important problems for these techniques.
That is correct, in fact you could also call it delta encoding.
I don't see how the same technique can be used with Bacula or any other
program that does not store the files in a directory tree on disk. These
techniques seem to require having the previously backed up file available for
comparison during subsequent backups. If someone has an idea how to
implement this without having backed up files online, please let me know.
Clearly the one big problem with delta comparesion is that to encode a
delta (find the difference) i a file you need a reference file (eg. the
last successful backup version) on the client. I have a few articles
that discuss the issue. The advantage of rsync is exactly that it don't
need a reference version on the client. I don't know the internals of
bacula system so I can't tell if it's a straight forward thing to
implement. But I would defenetly recommend it, as it's minimizing the
utilization of the network bandwide and the storage on the backup server.
Best regards
René Brask
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