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SNW: DAS makes a comeback as alternative to SAN, NAS

Industry watchers see storage directly attached to servers making a comeback, while others see a blurring of the lines between DAS and networked storage.

ORLANDO, Fla. — Discussion among attendees at Storage Networking World (SNW) this week has turned to a familiar topic—direct-attached storage (DAS). Serial-attached SCSI (SAS) and application-based data protection features are making DAS more viable, while scale-out systems could bring an emergence of a new converged infrastructure.

During a panel discussion about 6 Gbps SAS on Monday, representatives from Dell Inc., IBM Corp. and LSI Corp. said they see a strong demand for DAS from their customers. This demand is fueled by the advent of speedy small form factor SAS drives that can help cut costs.

"A 12-drive, 2U server can run a small database with less power and cooling and easier management than a SAN [storage-area network]," said Larry Hart, worldwide senior manager, Dell storage and networking product group. With 6 Gbps SAS coming, customers can attach dozens of drives directly to servers and re-create the performance of a SAN.

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Jacob Farmer, chief technology officer at storage integrator Cambridge Computer Inc., said on the show floor Tuesday night that clients are reconsidering DAS.

"The question is why you went to networked storage in the first place," he said. "If it was for I/O performance, you could probably buy the performance you need by bringing storage closer to the server CPU."

Application features such as Microsoft Corp.'s Cluster Continuous Replication (CCR) also mean SANs aren't required for clusters or replication. "These things are re-enabling DAS in some cases, but they're few and far between," Farmer said. "Most people want disk storage managed externally."

When DAS is good enough

However, some storage administrators say the old way of doing things are good enough for some applications.

"Six gig SAS really looks attractive, performance-wise, and it has dual ports like Fibre Channel," said Karl Lewis, storage administrator for the College of Engineering at the University of Michigan in Ann Arbor. "We're using a lot of big NAS [network-attached storage] from three-letter-acronym kind of vendors, but if we can't afford that, DAS lets us solve problems the way we want to solve them, either in a single box or a cluster."

Natalya Yezhkova, research manager with the storage systems program at Framingham, Mass.-based IDC, said DAS sales have been down the past two quarters. "But it was flat or showing modest single-digit growth over the three or four quarters before that," she said.

Despite cost savings, DAS isn't for everyone. "I'm glad I can look at my SAN management tool and get a central picture of our storage," said Kevin Fitzpatrick, IT director at ROEL Construction Co. in San Diego, who has Compellent Technologies Inc.'s Storage Center SAN.

Fitzpatrick said Microsoft has pushed DAS as his company looks to migrate to Exchange from Novell GroupWise email, but he's holding back. "I don't want to have the hassle with it," he said. "I'm also investigating hosted Exchange for that reason."

A "third way" emerging?

Even as some in the market talk about a DAS resurgence, defining DAS has grown trickier as the lines between storage categories are blurring.

Simply defining DAS as any storage attached to a server node doesn't quite fit when you're talking about clustered systems, pointed out Jackson Shea, technical lead, storage management at Portland, Ore.-based health insurance company The Regence Group.

"DAS makes me think of grids and small modular components," he said. "But is that really DAS or just modularization of networked storage?" Even if they're made up of DAS nodes, grid systems are managed as a single, shared entity. "All things being equal, I think everyone would rather just manage one object," Shea said.

Chris Watkis, director of IT at Grey Healthcare Group in New York City, said in a public session Monday that he thinks of DAS not in terms of hardware, but in terms of a one-to-one relationship between client servers and storage. What might be changing, he said, is the concept of SAN from a single centralized device into "a network process, rather than a hard and fast piece of technology."

SAS also blurs the lines a little between direct-attached and networked storage, said IDC's Yezhkova, because up to eight servers can share direct-attached SAS arrays. "It's not switched, but it's like a network," she said.

Hewlett-Packard (HP) Co. sees the two approaches to storage blending into a single infrastructure, according to Lee Johns, marketing director, entry storage at HP's StorageWorks Division. He said the company is preparing a software framework, based on its 2007 acquisition of Opsware Inc., to centrally manage different kinds of storage devices along with servers.

"We're starting to realize that storage is a software service that runs on top of an infrastructure of processing power and disk," Johns said.

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