Just raised this as a case under 1824707 but I'm sure it doesn't need hte full attention of a support rep, I swear I've missed something obvious.
Error I'm getting is :
Production datastore is getting low on free space (980.0 MB left), and may run out of free disk space completely due to open snapshots.
Now initially I can understand that this was valid, I'd provisioned a 500GB datastore and then configured it as a 500GB disk in the guest. However I've since expanded the datastore to 550GB, but left the disk at 500GB. Surely 10% free space on the datastore is enough :
So I reckon I must be missing something basic but I can't spot what. Any thoughts please?