Microsoft has revised its "No Exchange on NAS" policy to "No Exchange on non-Microsoft NAS."

For the longest time, Microsoft Exchange and network-attached storage (NAS) have been like oil and water, thanks to a Microsoft policy prohibiting the support of the combination.

It's not that Exchange wouldn't work over NAS, says Randy Kerns, senior partner with the Evaluator Group, "but if you have a problem, the MS Exchange group probably will only support you so far." Despite that, Kerns believes NAS is "a great option that requires less administrative efforts than the alternatives," and "translates to a lower cost of ownership and fits better into environments that don't have specific storage administrators."

Still, "people avoided doing [Exchange on NAS] because they wanted to avoid issues of finger pointing," says Tony Asaro, senior analyst with the Enterprise Storage Group. But this spring, Microsoft announced that it will in fact support

Exchange on NAS, provided that the NAS device is based on Windows Storage Server 2003, plus a recent Feature Pack, for environments up to 1,500 seats.

Where does that leave iSCSI, seen by many as the middle ground between direct-attached storage and a full Fibre Channel fabric? "You'll see both NAS and iSCSI," says Marcus Schmidt, Microsoft senior product manager for Windows Storage Server, as iSCSI storage is able to scale beyond 1,500 seats.

Already, EMC is promoting its latest NAS device, the NetWin 110, for Exchange environments of up to 500 seats. "The combination of NetWin and Windows Storage Server--as compared to proprietary NAS platforms--is Microsoft-certified to store Exchange databases and log files in a way that [Microsoft] wouldn't with another deployment mechanism," says Tom Joyce, EMC's senior director of NAS product marketing. NetWin can also be purchased with Legato RepliStor and NetWorker for replication and backup.

ESG's Asaro believes that EMC's NetWin will be very attractive to large organizations with branch offices, and limited IT expertise. "A Celerra [EMC's proprietary NAS offering] just doesn't make sense in these environments."