SAN/NAS convergence: proceed with caution

The many faces of convergence
Companies that are looking to combine SAN and NAS operations face a host of choices, including standalone NAS gateways, SAN solutions with integrated NAS functionality, NAS devices offering block I/O and even filer capability running within a switch.

Of these approaches, the most established is the standalone NAS device fronting a SAN disk array. The EMC Celerra NS600, IBM TotalStorage 300G and the NetApp F800 and FAS900 lines are all examples of NAS products that incorporate Fibre Channel (FC) ports on the backside to connect to a SAN switch. File calls over the IP network are routed through the NAS device and over the FC interface to the back-end file-based storage on the SAN array. In this arrangement, the NAS device acts strictly as a ramp onto the backend array for file calls. Host-based block I/O bypasses the NAS devices and goes directly to the FC switch.

The setup means that the NAS and SAN are managed distinctly and that volumes must be configured for block or file operation using independent tools. In addition, companies are typically limited to using a NAS gateway from the same vendor as the SAN.

An exception is the Hitachi Data Systems (HDS)/NetApp Enterprise Gateway, which mates NetApp FAS900 series filers with Hitachi Freedom Storage Lightning 9900 and Thunder 9500 storage systems. The solution is sold and supported by HDS, providing a single vendor point of contact for companies seeking to deploy the solution.

NetApp has gone further, however, by building arrays that provide both file and block I/O in the same array. The NetApp FAS900 family is an example of a device that has both a NAS head and a block interface and integrates block and file storage at a granular level (4k chunks), rather than the drive or volume level that gateways generally require.

The FAS900 series made its debut nearly a year ago as a high-end filer with high-end storage networking in the form of FC ports. Since then, NetApp has introduced iSCSI to the FAS line, and broadened it with entry-level products in the form of the FAS250 series, which integrates the filer head directly into the disk shelf, lowering cost and saving space. Initially, the 250 was an iSCSI-only hybrid box, but not for long.

"We have clear plans to enable the FAS200 series and the whole FAS line for Fibre Channel," says Rich Clifton, vice president for NetApp's SAN/iSAN unit.

NetApp's goal is to provide "unified storage"--block or file--on a common box, accessed via either the common Internet file system (CIFS), NFS over IP, FC, iSCSI or other protocols. In fact, the same data can be accessed via either FC or iSCSI. As it has rolled products out, NetApp is progressively enabling much of its ancillary software--such as its snapshot products--to work in file and block environments as well.

One implication of NetApp's approach is that it enables users to take a different approach toward optimizing their use of storage. For example, storage managers have traditionally put high-performance applications on a high number of small-volume spindles and low-performance applications on a small number of high-volume spindles. Many users are contemplating SANs that have two or three grades of storage arrays: a typical high-end box, a midrange array and a box full of serial ATA drives, for example, with access controlled through zoning or perhaps some form of virtualization.

A potentially simpler approach, according to Clifton, is to have dozens of high-volume drives. You can spread your high-performance data out across all of those spindles, gaining a performance boost, and still use the free space on each drive for low-performance data. That becomes more attractive the more the system automatically handles performance management, something NetApp prides itself on.

Hybrid capabilities in a single box may not work for companies already invested in a SAN infrastructure, but it's worth investigating for those moving from direct-attached storage (DAS). The capability also provides a ready upgrade path for those who now deploy NAS-only FAS900 devices.

The interoperability mess
Outside of rare partnerships like that between NetApp and HDS, the interoperability of SAN and NAS is weak, says Marc Farley, president of Building Storage, a consulting firm. "The existing products won't mix--it's oil and water," says Farley. "Forget about getting them to interoperate. If you want an integrated environment, at some point it is going to have to be a new environment."

In fact, interoperability is so poor that many companies are putting off integration all together. Ron Lovell, practice director for storage at consulting firm Greenwich Technology Partners, New York, NY, says concerns about vendor lock-in are top of mind among IT managers.

Even when products are supposed to interoperate, the results can be trying. Cadence's Forman says the finger-pointing on his converged SAN-NAS deployment got so bad that he had to throw out one vendor.

Forman says, "The finger-pointing gets insane. I think it went beyond finger-pointing and went to boulder throwing. We had some brutal meetings."

Forman's team struggled with what he termed "major compatibility problems with the SAN infrastructure," including host bus adapter (HBA) cards that failed to interoperate with FC switches. While the situation has improved significantly since 2001, crossing the gap between SAN and NAS still presents tough choices, says W. Curtis Preston, president of The Storage Group, a consulting firm in San Diego, CA.