Tried to
reorg rebuild
the whole table but not enough space in the database to do that
The only way I could fix it was to copy out the data, delete the data and re-insert it.
A truncate on the partition was incredably slow - I killed it before it completed.
I thought this would be quick its only 5000 pages - but having to update the global index means
the time for a truncate of a partition isn't much different from a delete.
(Obviously speed of page read is the most expensive operation)