Clustered NAS makes terabyte storage cheaper

Exanet has just released in the UK its highly scalable clustered NAS product, first announced a fortnight ago.

ExaStor employs Fibre Channel-connected (FC) disks and is built from a pair of Exanet Linux X86 server nodes, interconected by Gigabit Ethernet. The servers are connected to a storage array by Fibre Channel and two arrays can be used with an interconnect for server failover.

The storage is virtualised on the servers by Exanet applications that put a distributed file system in place across all the nodes in the cluster - something the company says is an advantage over NetApp.

Dr Giora Yaron, Exanet chairman and CEO, said: "NetApp bought Spinnaker. Why? They can't make their WAFL [NetApp file system] distributed. Customers have large files with five to ten [accessing] operators. Problem with NetApp is bandwidth." Exanet can ship the files to the people at the workstations faster through clustering and caching, the company claims.

Accessing systems see the NAS across a LAN where it is seen as a standard drive, be they Windows, Unix or Apple workstations. Exanet makes much of the Apple File Protocol support, with Yaron pointing out that neither NetApp nor BlueArc can offer the same. But NAS boxes such as the Dell PowerVault, HP StorageWorks, IBM NAS gateway and American Megatrends' do.

The Exanet NAS can be expanded by adding more nodes with each additional node having its servers on the server Ethernet network and thus forming a cluster. However the storage arrays in each node are not interconnected to the the storage arrays on the other nodes. There is no Fibre Channel switching between the nodes.

Files written to the NAS are split into sections and and spread across the storage arrays, thus speeding up file write time. When more than one client needs to access a file it is copied into that client's Exanet server memory as a cache. Each server pair can cache 8GB, meaning a 16GB file can be cached for faster access.

The number of nodes is said to have no practical limits. File sizes and file numbers are likewise said to be practically limitless.

Exanet is agnostic about disk drive types and interconnects. When Infiniband gets a working failover function then it could be used to interconnect the servers. The storage arrays could hold SATA disks if wanted. So far, four storage arrays have been qualified for use with the Exanet servers, including LSI Logic and StorageTek arrays.

Exanet's clustered NAS seems to have been conceived for customers with a need to have staff access and work on very large files one after another. Fast access to these files is crucial and Yaron reckons that customers with less than a terabyte of such files should stick with NetApp or their present supplier. Above that then Exanet is better value. The payback comes from greater user productivity.

Systems start from £17,000 and 1TB of storage. They are available from Kodak PolyChrome Graphics for graphics art customers and another suuplier is being signed up by Exanet for general commercial customers shortly.