Re: OK to take hourly snapshots, then cull older ones?

[David Madden <dhm@mersenne.com>]

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On 14-Oct-2013 21:53 , Roman Mamedov wrote:
> Sure, that's one of the more awesome uses of btrfs.
> 
> But keep in mind that old snapshots on the same FS are not to be
> used instead of a proper backup to external media/servers. If a
> block happened not to change for a year, and it gets damaged on
> disk, it will become damaged in all the snapshots all the way back
> to a year ago, and you lose that data.

I haven't looked at the wiki carefully enough to understand this, but
could one reasonably back up the snapshots of one BTRFS filesystem to
an independent BTRFS filesystem, in a more efficient way than just
dump/restore or cpio or something?

It sounds like you could rely on on-the-fly deduping to save space on
the backup filesystem, but you'd still be reading the whole source
snapshot tree and sending it to be deduped/written.  Seems like you
could improve things by just pulling the changed blocks from the
snapshot to the previous snapshot, which would (I guess) be the only
blocks actually _in_ the snapshot.

I guess what would really help is a "Best Practices Guide for BTRFS
Snapshotting and Backup."  Does anything like that exist?

Thanks,
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