A CDE Definition
A front end to disk storage that is highly scalable. A NAS gateway functions like a diskless file server with unlimited storage. Unlike the traditional "legacy" NAS device, which contains the file sharing protocol for access, the file system for storage and the disks themselves, a NAS gateway contains only the file sharing protocol and the file system.
The front end of the NAS gateway connects to the LAN over Ethernet. The back end connects to a RAID array via Fibre Channel or to a Fibre Channel switch, in which case the NAS gateway becomes a front end to a storage area network (SAN). Single RAID arrays can scale to several terabytes, but switches enable a large number of disk arrays to be attached.
Legacy NAS and NAS Gateways
When a traditional "legacy" NAS runs out of disk space or slows down due to a heavy workload, a new NAS device must be added to the network, and the file references in all the users' machines have to be remapped to the new drives. This administration headache is eliminated with a NAS gateway because it always presents users with a single folder interface to the storage. More storage can be added without reconfiguring anyone's computer. In addition, splitting a NAS system into gateways and disk arrays allows file processing and storage to be scaled independently of each other.
The ONStor Example
In 2003, ONStor (www.onstor.com) introduced NAS gateways that would work with any brand of RAID array and presented a virtual interface to the user. The workload could be redistributed among different NAS gateways without administrative changes in the user machines and without migrating the physical data. See NAS and RAID.
A NAS Gateway
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