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Microsoft says DAS helps cut Exchange Server costs

Got plans for direct-attached storage? With Microsoft Exchange Server 2007 replication features, like Cluster Continuous Replication, some Windows shops can avoid costly SANs for DAS.

As IT shops install Exchange Server 2007 SP1, one question they might ask is whether the cheaper and easier replication options available in the new server software should cause them to adjust their email backup strategies.

One goal of the Microsoft Exchange team is to cut Exchange Server's total cost of ownership. The way Microsoft plans to do it is not by lowering its licensing fees, but rather by showing its customers they can reduce overall storage costs by using direct-attached storage (DAS) instead of a storage area network (SAN).

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Benefits of SAN-based storage in Microsoft Exchange Server 2007
For months, Microsoft has been promoting via white papers the idea of using new replication features in Exchange Server with inexpensive DAS instead of more costly SANs. Some examples are How Microsoft IT Exceeds High-Availability Targets with Large Mailboxes at Low Costs Based on New Storage Designs and Planning for Large Mailboxes with Exchange 2007

There are certainly pockets of opportunity for DAS, which is an old storage technology that is connected to one computer and not necessarily accessible to other ones. Lately, the technology has improved in performance thanks to improvements to serial-attached SCSI, the protocol that moves data to and from computer storage devices.

Now as customers upgrade to Exchange Server 2007 SP1, it's a chance to revisit what sort of storage they want to use – either a traditional single copy cluster (SCC) on a SAN or Cluster Continuous Replication (CCR) and DAS, said Jon Orton, senior product manager of Exchange Server at Microsoft. "All things being equal, we recommend CCR over SCC," Orton said.

Indeed, the cost of running third-party storage is the biggest cost of running Exchange Server.

 In the case of disaster recovery, it's faster to back up now using CCR on DAS. With today's large mailboxes, backing up to SANs is time consuming and expensive
Howard Marks
Chief ScientistNetworks are our Lives
"If it costs $10 per user, per month on Exchange with a SAN back end, and if everyone who moves to a DAS model can save a dollar, then they can cut the cost of using Exchange by 10%, said Matthew Cain, an analyst at Gartner Inc., the Stamford, Conn.-based consulting firm.

With the release of Exchange Server 2007 in December 2006, and the move up from a 32-bit to a 64-bit architecture, IT managers were given a much larger cache, which reduced I/O bottlenecks. "Now when users retrieve information they don't have to go into storage," Cain said. "They just have to hit the cache."

IT shops can now get away with using larger, cheaper and slower disks because the demands on those disks are not as great. "If Microsoft can get everyone to move from SAN to DAS, it is lowering its cost of ownership, which is good for everyone unless you happen to be a SAN vendor," Cain said.

With the larger, cheaper disks, end users can afford to have large mailboxes. In the past, one barrier to having such large mailboxes is that if everyone had one it would take a long time to back up. To that end, Exchange Server 2007 added Cluster Continuous Replication, which backs up the Exchange store on another disk.

Recovering that disk is faster than recovering off of tape, Cain said. A user can pull a backup off of the copy on another disk, so if the long window [of time] for the backup starts to encroach during daytime hours, it's not a big deal. "You are not pulling off of a primary disk that impacts Exchange Server," he said.

Most IT shops today use SCC for backup, which is the traditional storage method found in Windows Server 2003. SCC is a clustered mailbox server that uses shared storage, such as a SAN, and all of the nodes of the cluster can access the shared storage. With the release of Exchange Server 2007, Microsoft had made some improvements to some of the set up processes and management in SCC.

CCR is expected to overtake SCC

Microsoft's Orton wouldn't hint about the future of SCC in the next version of Exchange Server. But he said he expects that more IT shops will choose to use Cluster Continuous Replication and its companion, standby continuous replication (SCR), which replicates data on a per-storage group basis to standby servers or clusters. SCR was released with Exchange Server 2007 SP1 earlier this year.

If Microsoft were to decide to remove SCC in its next version of Exchange Server, however, it will no doubt rattle customers if only because it would be a departure from the norm, which never makes IT administrators happy, said Howard Marks, chief scientist at Networks are our Lives, a Hoboken, N.J., consulting firm.

Marks added that these users will have to buy more disk drives because SCC only requires one disk drive. But even though you may need twice as much disk space with Cluster Continuous Replication, it is offset by the fact that DAS is less expensive.

"SCC was a high-availability model with a single point of failure and now that will be eliminated," he said. "In the case of disaster recovery, it's faster to back up now using CCR on DAS. With today's large mailboxes, backing up to SANs is time consuming and expensive."

But enterprises are all unique, and determining whether Microsoft replication and DAS makes sense will produce different results. There is probably no motivation for enterprises to abandon their current replication strategy, but Microsoft is certainly building a better case to use its replication, said Donald Leaman, a consultant at Glasshouse Technologies Inc., a Framingham, Mass.-based consulting firm.

"It gives the buyer something to think about," Leaman said. "Exchange just isn't about email, and maybe [IT shops] can better leverage what they already have. They may not have to do block-based SAN replication."

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