Unfortunately, I think the answer's yes:
# dd if=/dev/zero of=test bs=1M count=640 640+0 records in 640+0 records out 671088640 bytes (671 MB) copied, 0.396043 s, 1.7 GB/s # LODEV=$(losetup -f --show test) # echo $LODEV /dev/loop0 # blkid $LODEV # mkfs.ext4 -q $LODEV # blkid $LODEV /dev/loop0: UUID="f495c785-4b12-464f-b477-9320b1a1d3d7" TYPE="ext4" # btrfs-convert $LODEV creating btrfs metadata. creating ext2fs image file. cleaning up system chunk. conversion complete. # blkid $LODEV /dev/loop0: UUID="e872e338-ad47-4584-813f-ede58c734d4e" UUID_SUB="998cd182-5f72-4066-b419-fe7c381b608d" TYPE="btrfs" # losetup -d $LODEV # rm test # In the dump above the uuid changed during conversion. And btrfs-convert doesn't seem to have any useful command switches (from a quick glance @ it) that would prevent this.
Btw, Ubuntu's help wiki mentions (or, rather, implies) the uuid change during conversion from ext3/4, too.