Why Migrations Instead of In-Place Upgrades?

After a brief break from blogging, I was back in the studio recently recording more videos to answer questions about Exchange design decisions.

Now most of the time I talk to customers about new functionality that we have added to Exchange, and for the last few blog entries I have focused on some of these changes related to storage and archiving.

In this entry I wanted to cover another topic which gets asked about a lot – why did the Exchange team not include an in-place upgrade option in the product in recent versions? Is it that the Exchange team is filled with a bunch of lazy developers or are there valid reasons for doing this? 

I was going to stop there and let you watch the video (which I encourage you to do!) but I thought I’d give you a sneak peek into what the answer is, so here are some of the major points:

  1. Surprise! It’s not about the laziness of the Exchange Devs
  2. In major releases we tend to make substantial changes to our architecture to take advantage of exponential changes occurring on the hardware front. Doing this in a backwards compatible way often leads to substantial compromises that leads to a more expensive and less reliable TCO.
  3. Certainly to fully take advantage of the changes in the release requires rethinking the hardware design. Over the past couple of releases, doing this properly will reduce costs so substantially that continuing to run the old hardware would be un-economic even through it is fully depreciated.
  4. Given the rapidly improving hardware and the fact that the most expensive component (storage) wears out. Regular hardware refreshes in the order of every 3-4 years are needed. Doing both a major-version in-place upgrade followed by a migration to new hardware is a model that combines the worst of both approaches
  5. The migration model is well suited to most organizations because it allows you to move your least sensitive mailboxes first, your most sensitive mailboxes ( execs? application mailboxes?) last and have a great coexistence story.

The video covers a lot, including the online mailbox move feature. I'm interested in any questions or comments these answers generate. Let me know what you think.