Thanks for your suggestions rich. I did not mention DAOS because there is no duplication of attachments across the application, and DAOS does not (I stand to be corrected) assist with reducing the 64Gb limit (because you have the same problem in the event of having to un-DAOS - the abbreviated reason).
Deletion stubs are a good suggestion too. Deletions are being purged as per standard period. The application does not have any local replicas, so I will look at reducing this period.
I have heard of the defrag tool before but had not thought of it. I'll look into that and see if there are any improvements.
Appreciate the suggestions.
A