Re: Btrfs send with parent different size depending on source of files.

["André Malm" <admin@sheepa.org>]

Ok, but I don't want to keep old snapshots of the child volumes. Only 
the latest and then diffing it in regards to the master. Would that be 
possible?

On 2019-02-18 23:28, Chris Murphy wrote:
> On Mon, Feb 18, 2019 at 2:36 PM André Malm <admin@sheepa.org> wrote:
>> The reason why I'm using reflinks instead of snapshots is because the
>> master subvolume is large and will contain hundreds of gigabytes worth
>> of data. Now if I change / remove, say 10 GB worth of data from the
>> master subvolume unrelated to the child subvolume I don't want those
>> gigabytes sent down the wire with btrfs send as they are unrelated. Also
>> I want to be able to after time, when required, add more data from the
>> master subvolume to the child. Thats why I can't split the master
>> subvolume into parts of related data.
> OK, is it your plan to have both master and child on the destination
> Btrfs? So you plan to do a 'btrfs send' without -p option to send the
> entire master subvolume (snapshot) to destination first? And then you
> want to create the child efficiently using a difference between master
> and child? Yes I think that might work but I haven't tried it. But of
> course, master must already be on the destination.
>
> btrfs sub create master
> ##populate the master
> btrfs sub create childofmaster
> cp --reflink master/bunchoffiles childofmaster/
> btrfs sub snap -r master master.20190218-initial
> btrfs sub snap -r childofmaster childofmaster.20190218-initial
> btrfs send master.20190218-initial | btrfs receive /destination/
> btrfs send -p master.20190218-initial childofmaster.20190218-initial |
> btrfs receive /destination/
>
> However your subsequent incremental send/receive has nothing to do
> with master anymore; you indicate above you don't intent to keep
> master up to date on the destination. Just child. In that case the
> incremental changes look like this:
>
> cp --reflink master/morefiles childofmaster/
> btrfs sub snap -r childofmaster childofmaster.20190218T1905
> btrfs send child -p childofmaster.20190218-initial
> childofmaster.20190218T1905 | btrfs receive /destination/
> cp --reflink master/yetmorefiles childofmaster/
> btrfs sub snap -r childofmaster childofmaster.20190219T1301
> btrfs send child  childofmaster.20190218T1905
> childofmaster.20190218T1905  | btrfs receive /destination/
>
>