Yes, I'm blogging from the stage, and yes, I made it here in two hours, fifty minutes this morning....

So on my drive this morning, I was thinking about an e-mail I received yesterday.  A colleague forwarded some notes from a messaging evaluation team at one of our prospective customers.  They considered what the relative advantages of Domino vs. Exchange would be to them.  In their evaluation, they found that a disadvantage of Domino was the clustering model -- that it requires higher investment in disk vs. Exchange.

This puzzles me a lot, and not just because of the amount of caffiene and sugar I've had since 4:30 AM.  To me, redundant data would be a good thing.  If a storage unit in a clustered Domino server fails, another server takes over -- no interruption, no fuss, no mess.  In the Exchange/Windows clustering model, shared disk is required.  Less investment in disk, true, but a single point of failure.

To make an analogy, I have a set of spare keys to my apartment.  They're stored at a highly reliable location -- my mom's house.  It cost me a few dollars of higher investment to make a spare set of keys.  If I lose my primary keys, the good news is that it will only take me a few minutes to get back to normal and be able to enter my apartment.  If I didn't have a spare, I'd be paying a locksmith to restore my access -- taking money and time, including opportunity cost of lost productivity.  Wasn't the investment in spare keys a good thing?

Domino's clustering model is a lot more flexible, too.  You don't have to cluster every mailbox or application on a server -- you can establish different service levels for different types of users.  The cluster server doesn't have to be identical -- it can be an inexpensive Linux/Intel environment clustering with an iSeries.  It doesn't even have to run the same version of Domino.  Seems like all those options can offset the "higher investment" vs. the only realistically option in Exchange: active/passive clustering, on identical hardware, in an all-or-nothing scenario.

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