Microsoft IT Stops Using SANs for Exchange

For a while now, Microsoft and its larger consulting partners -- such as HP -- have been telling customers that direct-attached storage makes a lot more sense than shared disk arrays for their Exchange mailbox stores. This has been greeted with a certain amount of incredulity in some quarters. However, Microsoft has now put its money where its mouth is, so to speak.

Microsoft IT has always been a key player in the Exchange team's "dogfood" strategy (as in, "We eat our own dogfood"). So it was natural that it should follow the advice to ditch its expensive storage-area networks (SANs) and move to less expensive direct-attached storage.

The key was to make full use of Exchange 2007's continuous cluster replication (CCR) feature. CCR allows Microsoft IT to build clusters of mailbox servers that ship database logs in near-real time, so that there's always an up-to-date logical replica of the database available, should there be a hardware failure.

This does mean that Microsoft is essentially duplicating all of its mailbox hardware -- i.e, 50% of its servers are sitting almost idle, just maintaining a database replica and being a source of "nearline" backups. However, the economics are still attractive -- duplicating servers turns out to be less expensive than buying SANs.

For more on this topic, Microsoft IT offers this white paper, talking about its experience -- albeit in rather sanitized tones.

... Richi Jennings

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