Hubert Kario wrote:
On Tuesday 02 March 2010 03:29:05 Robert Collins wrote:
As I say, I realise this is queued to get addressed anyway, but it seems
like a realistic thing for people to do (use BackupPC on btrfs) - even
if something better still can be written to replace the BackupPC store
in the future. I will note though, that simple snapshots won't achieve
the deduplication level that BackupPC does, because the fils don't start
out as the same: they are identified as being identical post-backup.
Isn't the main idea behind deduplication to merge identical parts of files
together using cow? This way you could have many very similar images of
virtual machines, run the deduplication process and reduce massively the space
used while maintaining the differences between images.
If memory serves me right, the plan is to do it in userland on a post-fact
filesystem, not when the data is being saved. If such a daemon or program was
available you would run it on the system after rsyncing the workstations.
Though the question remains which system would reduce space usage more in your
use case. From my experience, hardlinks take less space on disk, I don't know
whatever it could be possible to optimise btrfs cow system for files that are
exactly the same.
Space use is not the key difference between these methods.
The btrfs COW makes data sharing safe. The hard link method
means changing a file invalidates the content of all linked files.
So a BackupPC output should be read-only.
jim
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