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How to tell your NAS from your SAN

Many server and storage vendors from Sun to Compaq are offering more SAN and NAS choices for their customers.

How to tell your NAS from your SAN
Rick Cook

Advancing technology and converging needs in the mid-range are blurring the distinctions between Network Attached Storage (NAS) and Storage Area Networks (SAN).

It used to be that a SAN was a specialized Fibre Channel network that attached pools of storage devices to one or more servers. A NAS filer was a box with a number of hard disks that plugged into the Ethernet LAN and served files over the LAN. A SAN was a complicated, expensive system that required expert design and installation while a NAS system quickly and simply added a chunk of storage to the network.

While the distinction is still obvious at the very low (NAS territory) and very high (SAN territory) ends of the market, the mid-range is becoming increasingly blurred. For one thing many SANs are eschewing Fibre Channel for gigabit Ethernet. For another, NAS filers are sporting more external storage devices and many of them now use a private network to connect to a tape library for backup or for other functions. Such NAS systems are more complicated to set up and configure than the plug-it-in-and-go NAS boxes. At the same time more vendors such as Compaq ( are offering SAN-in-a-box solutions, which greatly simplify setting up simple SANS. Finally more and more vendors, from Sun ( to Compaq are offering both SAN and NAS solutions.

In this area of overlap perhaps the most obvious rough-and-ready distinction is that, speaking broadly, a SAN provides information in blocks, like an attached disk array, while a NAS system deals in files, like a traditional file server. However the real point in that in this middle range the distinction between SAN and NAS is becoming progressively less important. In a lot of cases it makes better sense to think (and ask for RFPs) in terms of a 'storage system' rather than a SAN or a NAS.

Rick Cook has been writing about mass storage since the days when the term meant an 80K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last twenty years he has been a freelance writer specializing in storage and other computer issues.

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