Re: Incremental backup for a raid1

[Hugo Mills <hugo@carfax.org.uk>]

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On Thu, Mar 13, 2014 at 08:12:44PM +0100, Michael Schuerig wrote:
> 
> My backup use case is different from the what has been recently 
> discussed in another thread. I'm trying to guard against hardware 
> failure and other causes of destruction.
> 
> I have a btrfs raid1 filesystem spread over two disks. I want to backup 
> this filesystem regularly and efficiently to an external disk (same 
> model as the ones in the raid) in such a way that
> 
> * when one disk in the raid fails, I can substitute the backup and 
> rebalancing from the surviving disk to the substitute only applies the 
> missing changes.
> 
> * when the entire raid fails, I can re-build a new one from the backup.
> 
> The filesystem is mounted at its root and has several nested subvolumes 
> and snapshots (in a .snapshots subdir on each subvol).
> 
> Is it possible to do what I'm looking for?

   For point 2, yes. (Add new disk, balance -oconvert from single to
raid1).

   For point 1, not really. It's a different filesystem, so it'll have
a different UUID. You *might* be able to get away with rsync of one of
the block devices in the array to the backup block device, but you'd
have to unmount the FS (or halt all writes to it) for the period of
the rsync to ensure a consistent image, and the rsync would have to
read all the data in the device being synced to work out what to send.
Probably not what you want.

   Hugo.

-- 
=== Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk ===
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