Rsync

Pros:

• Can be resumed
• Progress indicator (kindof)
• Runs across ANY filesystem
• Easy to debug
• Tried & tested !

Cons:

• rsync-ing a running system is like booting a system after a power cut
• Rsyncing to a crappy filesystem might lose metadata
• You can’t realistically roll back without fs dependant hacks like hardlinks

Btrfs

A new entrant! Is it actually … BETTER than rsync?

Pros:

• A snapshot (to be backed up) can be made instantly on boot or on poweroff, when the files aren’t open
• Works nicely with systemd-nspawn so you can safely test mirrors of your filesystem
• Easier to roll back
• Can store more efficiently

Cons:

• You need to setup the snapshotting regime
• Complex, probably buggy and fallible (potentially dangerous)
• btrfs send cannot be resumed, so if you sending a backup somewhere remote and it’s interrupted… start again!