On Fri, Jan 04, 2019 at 09:27:33PM +0100, Georg Sauthoff wrote:
> On Sun, Oct 14, 2018 at 04:35:53PM -0600, Chris Murphy wrote:
> [..]
> > And now it replicates extents from seed to sprout. The copy is faster
> > than pvmove, rsync, dd, or rpm-ostree deploy.
>
> This sounds great!
>
> I just tried it (on Fedora 29), but those steps don't work for me:
>
> # cryptsetup --readonly luksOpen /dev/nbd0p4 tmp
> # mount -o noatime /dev/mapper/tmp /mnt/tmp
> # mount: /mnt/tmp: WARNING: device write-protected, mounted read-only.
> # btrfs device add /dev/nbd1 /mnt/tmp
> Performing full device TRIM /dev/nbd1 (4.00GiB) ...
> ERROR: error adding device '/dev/nbd1': Read-only file system
>
> Am I missing something?
Ok, a necessary condition for creating a sprout is setting the seed
parameter on the source filesystem (via btrfstune). [1]
(with the seed parameter a mount of that FS is automatically read-only)
Thus, this works for me:
# cryptsetup luksOpen /dev/nbd0p4 tmp
# btrfstune -S 1/dev/mapper/tmp
# mount -o noatime /dev/mapper/tmp /mnt/tmp
# mount: /mnt/tmp: WARNING: device write-protected, mounted read-only.
# btrfs device add /dev/nbd1 /mnt/tmp
Performing full device TRIM /dev/nbd1 (2.80GiB) ...
# mount -o remount,rw /mnt/tmp
# time btrfs device remove /dev/mapper/tmp /mnt/tmp
# umount /mnt/tmp
Best regards
Georg Sauthoff
[1]: btrfstune is also mentioned in the previously referenced
https://btrfs.wiki.kernel.org/index.php/Seed-device article
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