'Calculates the correct size for a thin pool.
Ideally we would use 100% of the containing volume group and be done.
But the 100%VG notation to lvcreate is not implemented and thus cannot
be used.  See https://bugzilla.redhat.com/show_bug.cgi?id=998347
Further, some amount of free space must remain in the volume group for
metadata for the contained logical volumes.  The exact amount depends
on how much volume sharing you expect.
:returns: An lvcreate-ready string for the number of calculated bytes.'

def _calculate_thin_pool_size(self):

    self.update_volume_group_info()
    return ('%sg' % (self.vg_free_space * 0.95))
