On Sun, Oct 14, 2018 at 04:35:53PM -0600, Chris Murphy wrote:
[..]
> Ha! I just realized after all this time that the Btrfs wiki does not
> make clear how to make a sprout, even though it mentions the more
> esoteric recursive seed.[1] Of course you can mkfs.btrfs, mount it,
> and send/receive. But send requires read only snapshots. Making a
> sprout is easier, you just remove the seed device. This is supported
> since 2009.
> 
> # losetup -r /dev/loop0 root.img
> # mount /dev/loop0 /mnt/
> # btrfs device add /dev/sda3 /mnt
> # mount -o remount,rw /mnt
> # btrfs device remove /dev/loop0 /mnt
> 
> 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?

Best regards
Georg
-- 
'NEVER USE A GNUPG VERSION YOU JUST DOWNLOADED TO CHECK THE
INTEGRITY OF THE SOURCE - USE AN EXISTING GNUPG INSTALLATION!'
    (http://lists.gnupg.org/pipermail/gnupg-announce/2006q4/000239.html)
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