Wednesday, June 22, 2011

Scale out NAS




      A traditional scale-up NAS box has a fixed amount of CPU, cache and drive slots. When it fills up, the customer needs to buy another device. Scale-out NAS systems appeal to organizations with huge files because of their potential for seemingly limitless expansion while still being managed as a single storage resource.


       Also known as clustered NAS, scale-out NAS originally took aim at applications requiring high throughput and high bandwidth, such as those in media and entertainment, high-performance computing, bio-informatics, and oil and gas.



     But these scale-out systems often weren’t tuned to perform well with the typical enterprise application, where EMC Corp. and NetApp Inc. held sway with their traditional NAS devices.



      Terri McClure, a senior analyst at Enterprise Strategy Group (ESG) in Milford, Mass, said scale-out NAS tended to excel in environments with fewer numbers of unusually large files rather than the large number of small files the typical enterprise has. That made them a good choice for pplications such as video streaming. But as scale-out vendors tune their systems to perform better with more I/O-intensive enterprise applications, their systems are starting to show up in more enterprise IT shops.



       Scale-out NAS got a major shot in the arm late last year when EMC acquired Isilon Systems. Isilon offers three options: its S-Series aimed at I/O-intensive smaller files, its X-Series for fewer number of large files and its NL-Series for bulk high-capacity and low-performance storage.



         Isilon’s 72000X has a maximum capacity of 10.4 PB in a single file system from a 144-node cluster. The company’s solid-state drive (SSD)-equipped S200 has a lower maximum capacity at 2 PB, but offers 85 Gbps of aggregate throughput and 1.2 million NFS IOPS in a single file system/volume from a 144-node cluster.
      Isilon claims its distributed file system-centric system was built from the ground up for scale-out storage, where  as systems that make use of a global namespace require a software layer for scale-out NAS.

      But Jeff Boles, a senior analyst and director, validation services at Hopkinton, Mass.-based Taneja Group, said the nuances of the architecture matter less to end users than the ease with which the system scales and whether multiple storage nodes can be managed as a single storage system.


         “Scale out is still very new and innovative and proprietary,” Boles said. “Because it’s not as simple of an operation as building a controller head on an array, you’re not going to see a convergence of technologies around one best architecture.”


    In addition to Isilon’s offering, other scale-out products include BlueArc Corp.’s Mercury and Titan Series Servers (which Hitachi Data Systems resells as the Hitachi NAS platform), Dell Inc.’s PowerVault NX3500 with a clustered file system acquired from Exanet, Hewlett-Packard (HP) Co.’s X9000 family (based on technology acquired from Ibrix), and IBM’s SONAS. NetApp has a cluster mode version of its Data Ontap 8 operating system (but not a clustered file system) and Quantum Corp.’s StorNext and Symantec Corp.’s FileStor are clustered file systems that run on hardware appliances.

         Greg Schulz, founder and senior advisor at StorageIO Group in Stillwater, Minn., said some scale-out NAS products increase the number of nodes for parallel performance or large sequential streaming, while others optimize for concurrent access of multiple small random file or page views. Some focus on data storage capacity, and others emphasize clustered file systems or clustered nodes, he said.


      More scale-out options are on the way. Dell, for instance, plans to use Exanet technology to add scale-out capabilities to its EqualLogic and Compellent SAN systems, according to Scott Sinclair, senior manager of Dell enterprise storage.


          NetApp’s Brendon Howe, vice president and general manager of the NAS business unit, added via email that the company’s next-generation Ontap 8 Cluster-Mode is designed as a scale-out version of its unified architecture that extends to enterprise applications and virtualized data centers.


       “We find that segmenting the scale-out discussion to just ‘NAS’ isn't that meaningful to customers,” Howe said.


        Randy Kerns, a senior strategist at Evaluator Group Inc. in Broomfield, Colo., said although there are situations where scale-out NAS makes sense, there are also plenty of use cases where customers will prefer simpler traditional NAS.


     “It may boil down to there’s a place for both,” Kerns said. “I think scale-out NAS and traditional NAS will both be around a long time.”

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