I kind of assumed it would be the case but any drive arrays created in the previous beta build of Home Server VAIL can’t be moved to the latest build…
The low-level data format for Drive Extender has changed with this release and is no longer compatible with data written by Drive Extender in earlier versions of Vail. Drives that were used as part of a server storage pool in an earlier version of Vail will show a status of incompatible version in the Hard Drives tab of the Dashboard. Incompatible hard drives can still be added to the default storage pool, but all data on the hard drive will be lost.
Fortunately I still have a 2tb spare disk to migrate data onto temporarily, so will do a rebuild tonight.