| Once seemingly headed to the great storage junkyard, DAS may well prove to be the classic car of the storage market as it re-emerges with improved performance and new Web 2.0-friendly uses.
DAS has hung around even after the advent of networked systems because it's cheap, easy to use and doesn't require nearly as much storage expertise as SAN management, making it much easier to find administrators for DAS.
"DAS is a huge part of the market and it gets no respect," says Lee Johns, director of marketing, Hewlett-Packard (HP) StorageWorks entry storage and storage blades. "Anytime anyone wants to talk about storage, they want to talk about the SAN." SAS drives replacing SCSI drives gave DAS a boost, he says. Johns says HP was seeing "a general sort of slow decline" in DAS adoption, but "the performance of small form-factor SAS drives has really helped" DAS pick up again.
"We're seeing innovation and growth in DAS business," says Praveen Asthana, global director of storage and networking at Dell. "[Vendors] are putting some storage functionality into the application itself." Asthana points to Microsoft Exchange 2007 as an example. "Instead of using a SAN back end, you can actually use a DAS back end," says Asthana.
Asthana predicts further DAS growth in the area of clustered software, where "the node doesn't have to be a smart product, it can actually be a dumb DAS product."
"A lot of credit goes to Google" for building a data center with DAS, says Milan Shetti, president at Ibrix. "If they had to deploy a Fibre Channel SAN infrastructure, it would be very cost prohibitive."
Shetti says large repositories are where Ibrix sees a lot of its customers' DAS implementations. "If they have billions of files to store, then the economics of DAS are mindblowing," says Shetti. He thinks improved DAS performance has also driven renewed adoption.
HP's Johns says DAS can eliminate issues of ownership that arise among departments using shared storage. He points to blade servers, solid-state drives and virtualization as technologies that may drive continued DAS use. "I think you're going to find a lot of innovative DAS-based storage architectures coming out," says Johns.
Dennis Ruane, senior database software engineer at Waters Corp. in Milford, MA, uses DAS in his test environments and for customers' biotech labs. These departments use DAS because it's cheaper and easier, and they like to control their own data. "Some companies we sell to don't always have SAN administrators," he says. "For installations limited to a certain size or number of lab instruments, you use DAS because it's easier to implement." And for testing, says Ruane, DAS isn't going away. "Because machines are spread out all over the place, I can't always get them in the SAN," he says.
DAS likely won't be retaking the data center anytime soon, though. Ultimately, DAS has the same limitations it's always had. "It works great if you only have a couple of servers, but once you start getting more than four servers, you can't even use it," says Dell's Asthana.
Kirk Martin, systems manager for Johnson County, KS, uses DAS with Symantec's Veritas NetBackup. "We were trying to venture into disk-to-disk backups and they were priced right and our backups are working well," says Martin. "We'll probably continue to maintain those for as long as we can get parts and service contracts on them."
Johnson County Unix administrator Mark Dietz says one concern they have is that their Sun StorEdge 3511 isn't being sold anymore, so support can be limited.
"So as you look at growing backup storage, it's a prospective problem," he says. "But I don't care what technology you buy today, it's going to be replaced in a couple of years and you're going to be in the same boat again."