DAS vs. SAN in Exchange 2007
I have spent a lot of time recently investigating storage solutions as part of a migration design for Exchange 2007.
The current implemented solution is a multi-node Exchange 2003 cluster with SAN based storage (No HA/DR). With Exchange 2007 the desire is to deploy a CCR/SCR solution to allow for data redundancy, disaster recovery, and site resiliency. The toughest decision that I have been faced with (given that I am not a storage guru) is in storage design. Should it be a DAS or SAN based solution? Each has benefits and negatives. Here are my random thoughts on the subject.
Traditionally storage has always been the bottleneck in systems hosting heavy IO applications like Exchange. With the transition to 64-bit in Exchange 2007, IO has been significantly reduced. This has allowed DAS (mainly Serial-Attached SCSI) to become a viable alternative solution for Exchange deployments.
SANs are very scalable but as they scale the TCO increases. DAS based solutions are able to scale less but at a much lower cost.
Any shared storage represents a single point of failure. Although it is rare for a SAN to fail, anything is possible. The HA and DR solutions offered by SAN vendors are generally very expensive and difficult to implement and support. The CCR/SCR solutions offered by Exchange 2007 in combination with DAS storage, offer a lower cost and easier to manage, high availability solution.
DAS based solutions can offer a significant cost savings over SAN based storage.
Some additional points to consider:
Footprint – DAS based storage array cabinets from most vendors (HP, Dell) that I have investigated, require 2U of rack space each. Any significant storage requirements would lead to significant rack space, power, and cooling requirements.
Administration – DAS allows for more centralized control of the storage configuration by the messaging team. The setup and maintenance is less complex than prior SAN configurations and does not include the need to rely on a storage administrator for assistance.
This is an interesting and important area to investigate as part of any Exchange deployment. As with any solution, a lot depends on what you current requirement is and future requirements are.