You Say SAN, I Say NAS

No matter what business your company is in, you're feeling the storage squeeze. Traditional storage architecture can't keep up with e-business requirements because it's tightly connected to a server or a mainframe. The need for additional storage capacity is driving the ongoing, rapid implementation of more sophisticated storage technologies among organizations of every size. It's time to decide whether you'll trust your company's data to network-attached storage (NAS), a storage-area network (SAN) or a combination of the two.

Orubeondo: With a NAS approach, the storage server is connected to an existing LAN. These NAS devices combine an optimized server with a large amount of RAID storage, and the resultant server appliance is easy to manage, fast and interoperable across operating systems. The key element of a NAS system is a filer, an optimized server dedicated to file service and storage; it's where the device's intelligence and file system resides. In a SAN, the file system resides on each host server.

NAS devices usually operate over IP running on top of Ethernet, while a SAN generally uses Fibre Channel. In a SAN installation, a high-speed Fibre Channel network is built to connect a group of storage devices to a group of servers. Each storage device is partitioned so that parts of the cabinet can be logically assigned to a specific server and file-system format, rather than true file sharing. A NAS approach is easier to implement and maintain than a SAN, not to mention less expensive -- prices are dropping even as the technology is booming. In contrast to a SAN, a NAS device is familiar and requires little IT staff effort. Management is accomplished via GUI in a Web browser, which enables easy NAS access from anywhere on the network.

Apicella: People are familiar with the NAS paradigm and are more likely to commit resources to it. They can be scared away from SANs because they foresee possible implementation problems. But vendors such as EMC Corp., Compaq Computer Corp. and IBM have implemented applications that let you manage storage allocation with very straightforward GUIs. Using a management console, you can easily and expeditiously copy and transfer logical volumes online from one host to another.

But I wouldn't say that SANs are more difficult to maintain -- quite the opposite! A SAN lets you focus on just your centralized pool of storage devices, whereas NAS devices can spread like mushrooms, driving you crazy by having to keep up with so many boxes.

A NAS method manages files; a SAN doesn't. A SAN manages units of disk space, which is how it provides storage for different [operating systems]. Think of a SAN as your storage factory that can build logical disks on the fly for mainframe, Unix and Windows machines, whereas NAS is just another file server.

Orubeondo: That's true, Mario: NAS was designed to be network-centric. But NAS is the preferred storage capacity solution for enabling clients to access files quickly and directly. NAS was developed to deliver a less expensive and less time-consuming way of consolidating storage and cross-platform file sharing on heterogeneous networks. Its main purpose is serving files to network users.

NAS systems aren't limited to read/write disk systems, but also include optical media systems such as CD-ROM and DVD-ROM servers. In addition to basic file service, NAS can be used for specialized tasks such as e-commerce, Web caching, local storage, remote storage or caching in [a hierarchical storage management] environment.

Because NAS servers are designed as storage devices, they are engineered for high performance, eliminating the bottlenecks users often endure when accessing files from a general-purpose server.

Generally, a NAS system's users will run HTTP-based and e-mail applications over the existing IP/Ethernet network. NAS users stick with the LAN because they have the network and know-how to operate it. They can achieve good performance from file-level commands and share files among servers and across OSes. NAS is more flexible than a SAN -- it lets you leverage current network investments and skills.

Apicella: True, NAS devices can deliver good performance, but only if the network can keep up. What if it can't? Isn't a better choice, from an architectural point of view, to have a network dedicated to storage traffic? A SAN is like having a lane on the highway completely dedicated to you.

With a SAN, you create your network infrastructure once and for all, making it easier to manage future growth. You can attach devices and servers to switches and hubs anywhere and anytime, and you can select storage-management applications that can cut administrative costs.

True, NAS can give you more space for your data, which is crucial, but NAS doesn't even scratch the surface of storage-management software and infrastructure problems.

Also problematic is the fact that most Internet companies are watching the window of opportunity for backups shrink. A SAN can provide relief because it lets you expand storage without limits, allocate space to any host and centralize the management using clever applications.

Show me a NAS unit that can supply data capacity for Unix, Windows and mainframes. If you have that big iron, a NAS probably won't do you any good. On the contrary, a SAN could turn out to be the only storage solution that your company will ever need, no matter how many different platforms you manage. The future is SAN, with maybe some NAS on the side.

The Networked Future

Orubeondo: One reason NAS exists is that the speed of the Ethernet-based LAN has caught up to the speed of the Fibre Channel-based SAN.

Gigabit Ethernet can provide a strong infrastructure for a NAS approach because of its backward compatibility with the already extensive base of Ethernet that uses older standards. Network managers can leverage their existing knowledge for managing and maintaining Gigabit Ethernet networks, which would include their NAS devices, existing fiber, hardware IP stacks and single chip transceivers. This backward compatibility would decrease the total cost of ownership associated with operating networks.

NAS trades some performance for manageability and simplicity, but it's by no means a lazy technology. Gigabit Ethernet allows NAS to scale to high performance and low latency, making it possible to support countless clients via a single interface. Many NAS devices support multiple interfaces and networks at the same time. As networks evolve, gain speed and achieve latency, NAS will become a real option for applications that demand high performance.

Apicella: What a NAS can do is impressive, but you didn't mention the word data once. That's because Gigabit Ethernet is a network protocol. A SAN's Fibre Channel is about moving petabytes of data back and forth. Both solutions use a network for data access, but NAS relies on the traditional Ethernet infrastructure, whereas SANs are typically built on a fiber-based network dedicated to data traffic. In the future, data and application traffic will probably require more bandwidth than Gigabit Ethernet can provide. If I'm not mistaken, Gigabit Ethernet's name defines its bandwidth limitation. But fiber quadruples that capacity to 4G bit/sec. -- and we'll need it.

Very soon, network managers will need to be able to define policies that say, "The response time for that application will be x milliseconds." Fibre Channel and SANs will eventually allow us to do that. Imagine management software working behind the scenes to deliver that performance automatically. Now that's what I would call easy data management.

Orubeondo: We will continue to see companies transferring their data to NAS devices and SANs. NAS and SANs share many common attributes. Both provide optimal consolidation, centralized data storage and efficient file access; both allow you to share storage among a number of hosts while supporting multiple operating systems at the same time; and both allow you to separate storage from the application server. In addition, both can provide high data availability and can ensure integrity with redundant components and RAID.

In migration scenarios, NAS is a steppingstone. In other scenarios, it's the best tool for the job. It would be a strategic mistake to view these networking architectures as an either/or proposition. When it comes to departmental, workgroup and enterprise storage, NAS and SAN both have a place.

Apicella: Although Ana and I tend to lean toward one technology or the other, real-world demands often require companies to support both technologies, at least in the short term. In fact, vendors such as IBM, Compaq, Dell Computer Corp. and Hewlett-Packard Co. are saying that the two technologies are complementary; they offer SAN and NAS solutions side by side. NAS is an immediate solution for a storage shortage, whereas SAN is a more comprehensive and strategic approach to storage management.

Orubeondo and Apicella are Test Center analysts at InfoWorld, from which this article has been reprinted with permission.

This story, "You Say SAN, I Say NAS" was originally published by InfoWorld.

Copyright © 2001 IDG Communications, Inc.

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