Erik Christiansen via luv-main <luv-main@luv.asn.au> writes:
On 18.12.15 22:45, Chris Samuel via luv-main wrote:
On Thu, 17 Dec 2015 11:06:10 PM Erik Christiansen via luv-main wrote:
I'm not grokking the benefit of doing the rsync _and_ a "cp -al".
The idea is to have snapshots over time, rather than a single snapshot. For instance as implemented in: http://rsnapshot.org/
[...] I didn't realise was that the links appear to be between unchanged files across backup versions, to save space.
It's around 8 years since I used an HP tape carousel for daily + weekly backups at work. Not doing that any more, so have devolved to just a couple of rotating snapshots, with no need to link between them to save space.
The active ingredient of rsnapshot is "rsync --link-dest", if you want to roll your own rsnapshot replacement. rsnapshot config mandates annoying literal tabs, has a directory structure that's not directly compatible with samba's Shadow Copy modules, and doesn't correctly handle a file being deleted, then readded (i.e. pass --link-dest to ALL snapshots, not just the last one). Or see btrfs/ZFS snapshots. These operate per block rather than per inode, so should be more effective and less failure-prone in edge cases (hint, there's an upper limit on hard link count). One thing rsnapshot does reasonably well is faking multiple tape rotations within the snapshot set. e.g. you say "1 yearly, 2 monthlies, and 7 dailies", and it works out which snapshots to expire. I don't know how to do that in btrfs/zfs land.