Re: Planning for subvolumes of subvolumes and btrfs send/receive

[Duncan <1i5t5.duncan@cox.net>]

Marc MERLIN posted on Sun, 20 Apr 2014 12:46:27 -0700 as excerpted:

> Long story short, I'm wondering if I can use btrfs send to copy sub
> subvolumes (by snapshotting a parent subvolume, and hopefully getting
> all the children underneath). My reading so far, says no.

I don't do much with subvolumes and absolutely nothing with send/receive 
myself, but from what I've read, no, for the simple case (but see below) 
that cannot work.

The reason is that snapshots (including the read-only snapshot done for a 
send) stop at subvolume borders.

In the large-internal-write-NOCOW-file dedicated subvolume case, that's a 
positive, since the dedicated subvolume can be used to avoid snapshotting 
the nocow stuff on the subvolume when snapshotting a parent, but in this 
case the same subvolume property is a negative.


Now somebody *DID* mention multi-subvolume sends, and indeed, checking 
the manpage, there appears to be allowance for that by naming multiple 
subvolumes (and multiple clone-sources when doing the incremental), 
*BUT*, there appears to be no corresponding allowance for multiple 
subvolume snapshotting, so your script would need a "for subvol in 
$subvols" type construct at least for the snapshotting, and once you do 
that, you might as well do multiple sends as well, as that's likely to be 
more robust than a the larger all-in-one send, if one of the subvolume 
sends/receives fails for some reason.

-- 
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