Vinum migration 4.x-5.4

[Robin Smith]

There seems to be a consensus in the references I've found that vinum
is completely broken on 5.4 and that gvinum/geom_vinum is not ready
for production use.  As it seems to me, this means that anyone using
4.11 (say) and vinum will have to abandon vinum (i.e. quit doing software
RAID) in order to upgrade to 5.4.  That can be both laborious and slow
(e.g. if you have /usr on, say, a four-drive vinum volume in 4.11, you're
going to have to replace those drives with something else in order to go
to 5.4.  Is that false, and is there a relatively simple way to get 
geom_vinum in 5.4 to read a vinum configuration produced under 4.11 and
start the vinum volume as it is?

Robin Smith