Like most people of the Lotus persuasion, I remember the days when advocates of Microsoft Exchange were very fond of stating that Domino was very wasteful of disk space because of it’s architecture – everyone has their own mail box and each e-mail (and it’s attachments) would be stored separately per mail box. So if I e-mailed 20 mb of file attachments to 10 users I’d be creating 200 mb of allotted disk space on the server(s). I’d also deserve to have my knee-caps broken.

Exchange on the other hand would save the file attachments once per server, resulting in much less space taken up… although the reality, so I understand it, was that the attachments would be saved once per storage group. Domino’s counter-argument was always that it’s architecture made it much more robust… problems to my mail box (which I’ve never had in 18 years) would not affect your mail box. But many are the stories of entire Exchange object stores suffering problems that take down mail access for all users for hours at a time. Domino advocates made statements long the lines of “disk space is cheap, down-time isn’t” – this is true, but there are cost of ownership aspects associated with large quantities of data (e.g. doing a back-up).

For Domino customers the big news of version 8.5 was the Domino Attachment and Object Service, otherwise known as DAOS. I’m sure that most of my potential audience know what DAOS is and does – it stores attachments once per server, therefore cutting down disk usage and also bandwidth usage. It also has performance benefits… if that large file is being written once to the disk rather than multiple times, the I/O will be reduced. Customers have been reporting reductions in disk space of up to 60%. All good stuff.

So what about Exchange? Well, while we’ve been moving in the direction of reducing the disk usage, it seems that Microsoft are pushing their customers in the other direction by removing single instance storage. An article on The Register references another article which states that the “change also reduces the overall size of Exchange databases”… but The Register conclude that “across a large enterprise with tens of thousands of Exchange users, there must be the potential for multiple tens of gigabytes of wasted storage space – if not terabytes”. Whatever, the overall theme seems to be more changes to the Exchange architecture, so no wonder in place upgrades aren’t possible. Meanwhile DAOS is something that’s optional and evolutionary to an existing and consistent Domino architecture.