Re: Incremental backup for a raid1

[Michael Schuerig <michael.lists@schuerig.de>]

On Thursday 13 March 2014 17:29:11 George Mitchell wrote:
> I currently use rsync to a separate drive to maintain a 
> backup copy, but it is not integrated into the array like n-way would 
> be, and is definitely not a perfect solution.

Could you explain how you're using rsync? I was just about to copy a 
btrfs filesystem to another disk. That filesystem has several subvolumes 
and about 100 snapshots overall. Owing to COW, this amounts to about 
1.2TB. However, I reckon that rsync doesn't know anything about COW and 
accordingly would blow up my data immensely on the destination disk.

How do I copy a btrfs filesystem preserving its complete contents? How 
do I update such a copy?

Yes, I want to keep the subvolume layout of the original and I want to 
copy all snapshots. I don't think send/receive is the answer, but it's 
likey I don't understand it well enough. I'm concerned, that a 
send/receive-based approach is not robust against mishaps.

Consider: I want to incrementally back-up a filesystem to two external 
disks. For this I'd have to for each subvolume keep a snapshot 
corresponding to its state on the backup disk. If I make any mistake in 
managing these snapshots, I can't update the external backup anymore.

Also, I don't understand whether send/receive would allow me to 
copy/update a subvolume *including* its snapshots.

Things have become a little more complicated than I had hoped for, but 
I've only been using btrfs for a couple of weeks.

Michael

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Michael Schuerig
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http://www.schuerig.de/michael/