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. 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
# 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?
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