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

["André Malm" <admin@sheepa.org>]

I assume i would have to use rsync (with --inplace possibly) to keep the 
master volume in sync between machines?

Say for example I have a (large) file on master, on machine A, I cp 
reflink it to a child subvolume. I then send -p child subvolume to 
remote machine B (which already have the master volume). Then i change 
parts of the file on the master of machine A. I then rsync (?) the 
master volume so its the same across the machines. Can I then later send 
-p the child volume, either back to the original machine (A) or to a 3rd 
machine (C) given that the master volumes are synced?

About the efficiency I'm not planning to remove large amounts of data 
that is used by child subvolumes (although some will be updated). But 
given the unpredictability of what files will be used by child 
subvolumes i might remove large unused amounts of data.

On 2019-02-19 00:49, Chris Murphy wrote:
> On Mon, Feb 18, 2019 at 3:58 PM André Malm <admin@sheepa.org> wrote:
>> 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?
> In order to do an incremental send/receive you need to have the -p
> snapshot on both source and destination file systems. You can delete
> snapshots older than that.
>
> I still don't understand why you're diffing in regards to master. It's
> going to be inherently inefficient because you've said a large amount
> of the contents of master aren't important; but by using it as the -p
> reference snapshot, you're asking send to do a comparison that
> includes a lot of metadata you don't care about. It's more efficient
> to diff the incremental snapshots of the changing state of
> "childofmaster" subvolume.
>