stable/13 and zfs <> openzfs

[Alan Somers]

On Tue, Feb 9, 2021 at 3:28 PM tech-lists <tech-lists at zyxst.net> wrote:

> Hi,
>
> I need to build a new zpool (arch=amd64). The machine needs upgrading
> from stable/12 to stable/13. The process I envisaged following is:
>
> 1. backup all data to a non-zpool disk
> 2. upgrade the OS stable/12 to stable/13
> 3. destroy the original zpool [1]
> 4. build new zpool and restore data
>
> stable/13 seems to have openzfs as the default zfs. Is there anything
> more I need do? [2] The system is havdling remote zfs receive from a
> 12.2-p3 system that uses the earlier default FreeBSD zfs. [3]
>
> [1] the original zpool was going to be destroyed anyway due to wrong
> ashift for these new disks.
>
> [2] like, does /etc/rc.conf need modifying? Things like that.
>
> [3] is the newer openzfs compatible with the older one? I mean will the
> older one still be able to send zfs snapshots for backup, or does
> something need to be changed at either end?
>
> thanks,
> --
> J.
>

The new ZFS is backwards compatible with the old one.  So your 12.2-p3
system will be able to zfs send, and the stable/13 will be able to zfs
recv.  You can go the other direction too, if you're careful to create the
new pool using the old format, and don't turn on any of the new features.

/etc/rc.conf shouldn't need any changes.

Your upgrade plan sounds fine.  But for the "backup all data" step, I would
recommend using zfs send/recv to do the backup.  That will do a better job
of ensuring your files' integrity than something like rsync or cp.

-Alan