Hi all,

I did find only a single reference to the topic- but already some years ago.

So are there any implications someone need to take care of when using
BackupPC pool on a BTRFS filesystem?

Some features of BTRFS seems to be perfect for BackupPC but I am unsure
if they have advantages.

Deduplication feature:
BackupPC hadrlinks identical files to save storage space which is
already deduplication. But it uses hardlinks to do so- which frequently
causes issues as you can see in this mailing list. So possibly diasble
hardlinking in BackupPC (if possible) and let BTRFS do the work with
deduplication? Disadvantage for BTRFS: it is only a "out-of-band"
deduplication- so you have to perform the dupe detection by cron or so.

Online-Compression:
BTRFS uses online-compression- I am unsure if there would be an
advantage if compression is done by filesystem. At least IMHO it would
be easier to restore directly from the pool instead of cpool through bash?

Pool-migration/ move:
If you decide to move your pool to a different location you are happy if
you have it on something like LVM (or completely virtualized). Then you
can move the underlying device. Disadvantage: LVM and other tools move
the full device. If the pool is just filled up to 70% it even transfers
the 30% of empty space. With btrfs receive and btrfs send the filesystem
will only transfer the used blocks.

COW-Feature:
With copy-on-write btrfs writes changed block on a different location
and then refers to this new location. Has advantages for snapshots and
so on. But disadvantages for larger files (like virtual disk images) as
they spread among all devices which causes lots of seeks on rotating
devices like HDDs. How about pool? Am I right this does not matter for
backupPC as it always writes full files only? Even rsync-based backups?

Besides of BackupPC someone havving experiences in using BTRFS?

Thanks!

Christian






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