Recently Techworld has written about several virtualising network-attached storage (NAS) suppliers and their products. In the clustered product area we have looked at both OnStor and Isilon.

Jon Toor, VP of marketing at OnStor, discussed some of the differences between OnStor's Bobcat clustered NAS product and the Isilon range.

Toor said:" Bobcat consists of a 1U-high rack servers running UNIX. These are n-way clustered for scalability and high availability, growing to 8 nodes within a cluster. From the user’s perspective, the device appears to be a conventional NAS device, serving files to Windows, Unix and Linux clients."

With the Bobcat 2280, integrated n-way clustering capability allows aggregate throughput to grow linearly to 1.2GB per second as NAS Gateways are added to the cluster. The 2280 has 64-bit network processors and a FastPath chip which accelerates throughput to up to 300MB/sec.

How does Bobcat differ from ordinary NAS boxes? Toor said:" There are two elements that distinguish it from conventional NAS. These are, firstly, open storage. It serves files, stored on multi-vendor storage arrays and supports five times more storage types as the closest competitor. Secondly, scalability; it grows in a single storage pool, and with a single pool of processing resources."

The multi-vendor storage array feature is different from Isilon's approach where nodes have Isilon-supplied disks and are generally combined processing and storage nodes. You can though, add disk-less processing nodes to an Isilon cluster to scale performance independently of capacity. You could also add a processor-less disk expansion unit to scale capacity alone.

OnStor provides NAS gateways that can be clustered, using Ethernet, and access back-end SAN storage across a Fibre Channel fabric. Isilon provides NAS nodes that can be clustered, using Infiniband. Both provide a single virtualised NAS storage pool. Both allow access from any NAS gateway (OnStor) or any node (Isilon) to any data anywhere in the namespace (storage pool). Data is accessed from application-running servers over Ethernet in both cases.

Toor pointed out several divergences from Isilon's approach. In his view: "The Isilon product is suited to streaming applications and large file transfers. But it does not scale well on random throughput - they do not even publish SPEC numbers. Random is the most common workload in general purpose file services, and is the environment where OnStor delivers linear performance scaling."

As far as SPEC sfs numbers are concerned Toor was pleased to point me towards results for a combined OnStor/3PAR test run. The OnStor/3PAR combination demonstrated the fastest open NAS gateway test score ever reported by the Standard Performance Evaluation Corporation (SPEC), doubling the fastest performance reported for Network Appliance's open storage NAS gateway. With 128,236 SPECsfs operations per second from a cluster of four OnStor 2260 Bobcats, OnStor's NAS Gateway delivered a three-to-one price/performance advantage compared to open NAS gateways from Network Appliance.

(In addition, the InServ Storage Server used to obtain this result was running 3PAR Thin Provisioning software, which features unique dedicate-on-write technology that enables 100 percent utilization of dedicated raw capacity versus 30 percent with traditional dedicate-on-allocation technologies.)

Toor then turned to open storage concepts, saying: "Isilon storage is built-in to the nodes. You add storage by adding nodes, which is a) expensive, and b) not open."

A third point is that Isilon has: "Limited support for Windows clients (and is) not well-suited to large-scale Windows environments."

What Toor is saying is that OnStor's products are better-suited than Isilon for file-serving applications which are non-streaming and/or are operating on randomly-sized files. OnStor and Isilon compete in the large file streaming area and there, Toor is saying, there is no independent performance comparison possible until Isilon publishes SPEC sfs results.