What model and os version is your 3PAR?
We noticed something recently when migrating from an older 10400 3PAR with 3.2.2MU4 to a new 9450 3PAR with 3.3.1MU3, we had a 100G LUN on the 10400 and a 100G LUN on the 9450. It appears the geometry defaults changed even within 3PAR models/versions as the heads/cylinders etc were different and the number of bytes/sectors did not match (the new LUN being a little smaller) so trying to mirror a byte for byte copy in Solaris complained.
EDIT: There are options at the CLI I think to manually specify the LUN geometry which might get around this but I've avoided going there and our UNIX admins seem to have worked around the issue at their end without me having to tweak LUN sizes.