A convergence of networked storage architectures is approaching - and the hope is that we'll get the best from both the storage-area network and network-attached storage worlds.
As far as storage vendors are concerned, data will grow in one of two ways: as data that should be accessed in blocks, and as data that should be accessed in files. Generally speaking, file-accessed data is placed on NAS devices that act as file servers, and block-level I/O takes place on SANs.
There are lots of NAS products out there. In many instances managers buy low-end, barebones NAS boxes, and have enjoyed the immediate benefit of their commodity pricing. Not too far down the road, however, these things become like tribbles and proliferate the IT center. Because these devices are relatively small, in many cases they get no management at all.
The marketing spin from vendors is that this is flexible, distributed storage. But IT managers come to view these things as small storage islands, often less manageable and certainly no more endearing to them than the larger SAN islands they are also struggling to control. The trouble with tribbles, as any Star Trek fan will tell you, is that they keep multiplying.
NAS gateways seem to offer a way around this. Such gateways are special-purpose NAS devices that provide IP access to SAN storage capabilities. Behind the NAS front end is a SAN, with any mixture of storage devices that you might expect to see on a storage network, including RAID boxes, JBODs and, conceivably, even direct-attached storage. The idea here is that hanging a SAN off a NAS is a useful way of providing the scalability, flexibility, manageability and higher availability we have come to expect from the pooled storage within a SAN, but still make use of existing infrastructure. It sounds like a useful way to consolidate all those islands into a few continents, and should be welcome in situations where data would be accessed through a networked file system.
With such devices, islands would still exist (if you utilized more than one such gateway), but there would be far fewer of them because each one front-ends a much larger storage pool than was available before.
What should you look for in such devices? The features should include mirroring; backup software; the ability to provide point-in-time copies; excellent performance for HTTP, NFS and CIFS; and a level of reliability that maps appropriately to your needs. iSCSI would be nice too.
Expect NAS gateways to be easy to deploy, just like a NAS device should be, and to make further storage expansion easier. But the greatest value is likely to come from the improved levels of manageability when compared to the manageability of NAS data strewn around the enterprise.
Such devices include EMC's Celerra, HP's NAS 7000 and 8000, and several products from NetApp (also resold by Hitachi). These are robust machines that offer all sorts of internal and external capacity, and can provide you with a means to consolidate all those tiny islands of storage into a few bigger islands - or maybe into one enormous tribble.