"We've migrated many of our disparate storage islands onto our SAN, but some of our systems just aren't good candidates for the move," said Gonzales, who is the senior network administrator at the Denver-based financial institution.
He's found that DAS, which hooks directly onto a server, is a better choice than SANs in three specific cases:
- Where putting the application on the SAN would require too much expansion of the SAN with little to no return on investment
- Where the legacy nature of the application and its storage won't allow for integration with the SAN's iSCSI or Fibre Channel data fabric
- Where the application or server data has a low enough recovery time objective (RTO) or business value that it's not worth the money or time to move the data over to the SAN, such as a testing and development environment
As an example, he points to the credit union's primary line-of-business financial application, which is SCSI-attached and therefore still requires DAS.
The benefits of direct-attached storage
While staying with DAS may seem like a hardship because of the tremendous growth in SANs, industry experts say DAS technology has also matured in both hardware and management tools and offers its own rewards.
"DAS's biggest benefit is that it gives SMBs easy-to-use storage and storage management in a single box," said Mike Karp, senior storage analyst at Enterprise Management Associates. "In some cases, it's even faster than if you deployed a SAN."
Ray Austin, director of storage product marketing for Sun Microsystems Inc., agrees. "DAS has this old connotation that it's limited and non-scalable. That's just not true. DAS is making a comeback because some SMBs want the benefits of a SAN, such as backup and recovery, without having to deal with the complex issues involved with testing and managing them," he said.
Many of today's DAS products feature fault-tolerant, high-availability architectures atop hard disks, CD-ROMs, tape drives or portable USB drives. They also include data protection, such as policies and encryption, to help SMBs comply with security and privacy mandates.
The ability to get all this functionality at a relatively low price is part of the draw for SMBs, according to Harold Pike, team leader for entry and mid-range disk at IBM Corp. "In this economic climate, SMBs are maniacally focused on the acquisition cost, not the total cost of ownership, of storage, and DAS has the lowest acquisition cost," he said.
He adds that with layoffs, SMBs might not have the storage expertise on staff needed to run a SAN. "DAS definitely is easier to implement and requires less skill sets in your IT team," he said.
While simplicity is critical for SMBs, DAS is also attractive for its inherent speed. "Organizations running large databases may intentionally deploy DAS because of the performance advantages gained from direct attachment," said Ted Ritter, analyst at Nemertes Research.
That's the logic that has kept the Northwest Radiology Network in Indianapolis using DAS for its picture archiving and communications system, said director of IT Marty Buening.
"We capture large, high-fidelity images from the radiology equipment, such as MRI machines, and send them off to the storage system. They have to be viewed in a fast fashion by our radiologists so we need incredible disk I/O performance. We get that from DAS," he said.
The team uses IBM's DAS technology, which attaches to the picture archiving and communications system server via SCSI connections to a RAID-based disk cabinet with five 1.4 TB nodes.
Buening, who has deployed SANs elsewhere in his network, predicts DAS will back his imaging system for the foreseeable future. "Because it's a specific, data-intensive application, you don't want the network to become the bottleneck," he said.
Gonzales, who uses a mix of DAS vendors such as Dell in his network, also doesn't see the need for DAS diminishing. "For smaller businesses, the true strength of DAS -- compared to SANs -- is its "set it and forget it" reliability. Therefore, any time your data storage needs are predictable, finite and larger than what is reasonable for a personal drive, DAS is your answer," he said.
Sandra Gittlen is a freelance technology editor in the greater Boston area. She can be reached at firstname.lastname@example.org.