SAN is less expensive than DAS for all on premise Microsoft Exchange installations with more than 500 seats, or that are likely to grow above that level, or installations of any size that require high availability, writes Wikibon CTO David Floyer in “Revisiting SAN vs DAS for Exchange 2010.

This is a significant change from Wikibon’s initial analysis in 2010, at a time when Microsoft was pushing DAS for Exchange installations below 800 seats to make it cost-competitive with cloud Exchange services. At that time Wikibon’s analysis basically agreed with Microsoft’s published figures.

Since then, advances in SAN technology coupled with the increased demand for high availability have changed that picture. Today, he says, Wikibon would only recommend DAS as a less-expensive alternative for non-growth environments of less than 400 seats that can tolerate the risk of occasional, unplanned long outages. For everyone else, SAN is the answer.  See here for more info and ongoing discussions around SAN.