In lvm2 version 2.02.105 lvconvert gained a --splitsnapshot option to
allow people to wipe snapshot content before releasing the extents
for reallocation.
--splitsnapshot
Separates SnapshotLogicalVolume from its origin. The volume
that is split off contains the chunks that differ from the ori-
gin along with the metadata describing them. This volume can be
wiped and then destroyed with lvremove. The inverse of --snap-
shot.
Alasdair