New Life in Old DAS


Direct-Attached Storage (DAS) may have some mileage in it after all now that new generations of SAS technology make it possible to bring the devices into networked storage architectures.

The writing had been pretty much on the wall for DAS since virtualization started to take hold in the enterprise. The vast storage needs of multiple virtual machines made it practically impossible for DAS to exist outside of specialty shops or very entry-level installations.

But now that solutions like LSI's SAS6000 6 Gbps switches are hitting the channel, DAS stands a viable chance of at least playing a role, although not a dominant one, in the emerging era of converged storage networking. The 6000 is a small (1U and less, depending on configuration), rack-mount device that provides 16 24 Gbps SAS connections, delivering a total bandwidth of 383 Gbps. That should let you network upwards of 1,000 drives using either SAS or SATA connectivity, with space left over for such housekeeping tasks as domain management, port configuration, zoning and diagnostics.

The possibilities of networked DAS are not lost on data center platform providers like Dell. The company recently added an end-to-end 6G SAS solution to its PowerEdge portfolio, including new RAID controller cards for the 11G server line and new higher-capacity PowerVault models. The company says the new line will double throughput and deliver a third more IOPS, as well as provide for improved load balancing through redundant path support and other techniques.

At the same time, drive manufacturers are paying increased attention to their SAS drives in the hopes that the combination of greater capacity and higher throughput will cause enterprises to place more storage next to the server. Toshiba, for one, expects the majority of its new 2.5-inch, 10k SAS drives to act as DAS storage, which the company says can help save on data center space and power consumption. The 600 GB MFB drives are the first to hit the channel since Toshiba's acquisition of Fujitsu's hard-drive line.

Despite all the good feelings, however, the world is still rife with stories of organizations dumping DAS for SAN or NAS and thriving. UK credit data firm CMA, for one, reports an annual savings of 500,000 pounds (roughly $US763,000) after swapping its DAS-based cluster architecture for a virtual server/storage infrastructure based on Compellent's Fluid Data storage system. As the credit industry increasingly demands real-time performance, the company says, features like automated tiered storage are proving invaluable.

Clearly, DAS has a way to go before it can be viewed as an equal partner to SAN or NAS. But it is a relatively low-cost solution that may act as an interim step toward full-scale storage networking at growing organizations.

At the same time, the new-found networking capabilities means you can still leverage your old DAS devices even after you've made the switch to virtual infrastructure.