I'm doing a big upgrade on my computer and I tryed to use lv mirroring
to obtain a copy of my data before to do it.
As I do with LVM on other OS i thought that after mirroring one could
chose to split the mirrored lv.
I can't find how to do it with LVM2 on Linux.
snapshot may be a good fit in this case, but if you insist you can use
lvconvert to convert your linear volume to a mirrored volume. Once the
sync is complete, you can use the same lvconvert to convert the mirror
volume to a linear one.