Re: Copying a btrfs filesystem from one host to another, reflinks, compression

[Andy Smith <andy@strugglers.net>]

Hi Andrei,

Thanks for your reply.

On Thu, Dec 05, 2024 at 07:11:59AM +0300, Andrei Borzenkov wrote:
> 05.12.2024 01:24, Andy Smith wrote:
> > rsync or tar | ssh | tar are not going to handle reflinked files,
> > are they?
> > 
> > Should I be using btrfs-send?
> 
> btrfs send/receive has better support for sharing data between files, yes.
> It is not guaranteed, that destination will have exactly the same data
> layout though; btrfs send may decide to send full data instead of sending
> clone request. I am not sure about exact conditions, IIRC one requirement
> for cloning is proper alignment.

Hmm. I don't mind if the destination has a  bit of a different layout
but I would not like if a significant number of the regions on the
source got deduplicated…

I guess I will have to try it and see what happens (time-consuming,
given the size).

If it expands too much I may have to try again with dd.

> > Would that preserve compression or would I have to go through and force
> > recompression of everything?
> > 
> > Source host's kernel is 5.10.0-32; btrfs-progs v5.10.1 (Debian 11).
> > Destination would be Debian 12 so kernel 6.1.0-28 and btrfs-progs v6.2
> > 
> 
> According to man btrfs-send, --compressed-data should preserve compression.

Looks like I would have to install a newer btrfs-progs on the sender as
I read in:

    https://btrfs.readthedocs.io/en/latest/btrfs-send.html

    --proto <N>

    Version 2 requires at least btrfs-progs 6.0 on both the sender and
    receiver and at least Linux 6.0 on the sender.

    --compressed-data

    This requires protocol version 2 or higher. If --proto was not used,
    then --compressed-data implies --proto 2.

Thanks,
Andy