SAN and NAS: Better Together

When deploying Windows servers, administrators commonly attach disks directly to each server. For example, the Windows & .NET Magazine environment has separate servers for editorial, production, sales, human resources (HR), and finance, and each of those servers has its own storage.

One problem with this approach is that accurately predicting how much storage each group of users will require is difficult. Consequently, administrators often start out by attaching 100GB of storage, for example, to each server. Within months, however, one department might be using 90 percent of its storage while another is using only 20 percent. Because reallocating storage from one department to another in a Direct Attached Storage (DAS) environment is difficult, most IT departments simply add disk storage as necessary to those servers that need it. According to industrywide research, as much as 70 percent of DAS is typically wasted because it's improperly allocated and too difficult to reallocate.

In addition to the problems of reallocating DAS, the quota-management software that comes with Windows 2000 Server lets you control the amount of storage per user but not the type of files that a user can store. A poll of attendees at a recent Windows & .NET Magazine storage Webcast found that in most cases, more than 30 percent of files saved in DAS environments were non–business-related junk files, such as MP3s. In other words, according to that poll, almost one-third of the disk space that corporate IT purchases and maintains is used for non–business-related files.

Storage Area Networks (SANs) and Networked Attached Storage (NAS) let you easily add or reallocate storage and prevent the storage of nonbusiness file types. SANs are optimized for the high-volume block-oriented data transfers typical of databases and application servers; NAS is optimized for file serving. Consequently, SAN and NAS are often thought of as mutually exclusive technologies. However, SAN and NAS actually complement each other and can be combined to solve common IT storage needs.

SAN vs. NAS
In the simplest terms, NAS is an optimized file server that connects directly to an existing network and serves file data to clients on the network. In contrast, a SAN houses application server data on a dedicated, high-speed network, usually Fibre Channel—based, that serves data to multiple application servers on the dedicated network. Your OS views NAS storage as physical storage, so if you add 500GB of NAS, it appears as 500GB to the OS. SAN storage is divided into logical units, each of which is identified by a LUN. The Windows network sees only the LUNs for the units that you've configured and made available to your network. Table 1 summarizes the major characteristics of NAS and SAN, and Table 2 shows some typical uses for each technology.

But what can you do if—like most midsized to large companies—you have some requirements that would be best satisfied by using NAS and others that seem to call for a SAN? For example, maybe you have old Windows NT servers that handle file serving as well as Microsoft Exchange Server 5.5. You want to migrate both your file and application data, move the appropriate file-access security, create the associated Active Directory (AD) entries, and move the data into Exchange 2000 Server on a Win2K or later server. In this scenario, NAS is the best approach for your file data, and SAN is the optimum solution for your Exchange server application data. In fact, a Windows Powered NAS (WPNAS) device won't let you run Exchange data on it, so your only choices for Exchange data are a SAN or a general-purpose file server.

In such a scenario, you basically have three choices:

Like a hammer and a nail, SAN and NAS are designed to do different things but can be used together to great effect. Figure 1 shows how the fusion of SAN and NAS in an Exchange environment might look. Clients connect to NAS through a standard IP Ethernet network, and the NAS and Exchange servers connect to the SAN through a dedicated Fibre Channel network. Unlike either approach used alone, a fusion solution is optimized for both file and application server data.

NAS Heads
A NAS head is a protocol handler gateway to a SAN. Having only enough drives to boot the WPNAS OS, a NAS head uses the SAN for disk storage. In the case of a WPNAS head, your SAN appears as a standard Windows-based server, and all Microsoft and third-party storage-management tools, virus checkers, and Group Policy Objects (GPOs) work as if they were attached to a standard Windows-based server. This compatibility also extends to AD support.

A NAS head lets you leverage your SAN investment for file-server consolidation. For example, Continental Airlines consolidated 14 NT servers onto four clustered WPNAS heads that front a SAN, then migrated both file and application data to the SAN. Each NAS head provides failover and load-balancing capabilities and does all the protocol handling necessary to move data from file-level access to block format and back again. Users access file and applications data as if it were on a huge Windows server. And because the data is stored on a SAN, administrators can use all their high-end management tools as well as off-the-shelf Windows server utilities from Microsoft and third parties. Another benefit of a NAS head is that Windows-oriented administrators can leverage their existing knowledge by using Win2K-based utilities to manage much of the SAN.

Here's a word of caution that you should keep in mind when you're shopping for a solution: Only WPNAS heads provide complete Windows server functionality. Other NAS heads provide some of the same functionality but don't emulate a pure Windows server environment. For example, an administrator might not be able to run typical Windows server management utilities on a non-WPNAS head.

Although NAS heads have been around for only about 18 months, they already represent 10 percent to 12 percent of overall NAS product sales. Some analysts predict that more than half of new SAN installations will include a NAS head because of the increased functionality it provides.

As a result of this trend, several storage manufacturers have created combined SAN/NAS solutions. For a list of manufacturers who currently offer combined solutions, see "Contact the Vendors." Expect other manufacturers to follow suit. Combining a SAN and NAS in one storage solution

The Case for NAS
If a combined SAN/NAS solution is so great, why would anyone ever buy a SAN or NAS alone? I can't think of a reason to purchase a SAN without a NAS head, but many scenarios still call for a NAS device by itself.

NAS is perfect for companies that have numerous remote offices running typical office applications, such as Microsoft Office. Each remote office could have its own NAS device. Assuming the remote offices are connected to a centralized office by a WAN connection, you could connect each remote office NAS to a centralized NAS rack and replicate the data in real time using a tool such as NSI Software's Double-Take. Using replication software, you could back up all the remote offices from a central location instead of putting a backup tape drive at each remote site. You could also replicate the central NAS rack to an offsite location to provide a high level of business continuity in the event of a disaster. Then, even if the central office were offline, the replicated disaster-recovery hot site could continue to serve the remote offices.

Another scenario for a NAS-only solution might be a small office that simply can't afford the price of an entry-level SAN. Small offices require storage that's easy to install and that consultants can manage remotely without the aid of onsite IT staff. In a situation such as this, WPNAS provides a perfect storage solution: You can attach a WPNAS device to an existing network in about 15 minutes, and you can manage it remotely through a Web browser. For a summary of WPNAS features, see Market Watch, "Windows Powered NAS Solutions," April 2003, http://winnetmag.com, InstantDoc ID 38274. That article also lists WPNAS vendors and products.

Peering Into the Future
NAS heads are the fastest growing segment of the storage market. This growth will lead to a proliferation of combined SAN/NAS storage solutions. In the not-too-distant future, I expect all SANs to have an integrated NAS head option.

Only a few years ago, the typical SAN installation cost more than $1 million and was affordable only for ultra-enterprise customers. Today, the entry-level price is approaching $25,000, and SANs are finding their way into midsized companies.

As I mentioned earlier, SANs are configured into logical units, so one SAN can support multiple servers. In contrast, today's NAS devices are configured into physical storage units, which attach to an existing network. Although adding storage to an existing NAS is easy, you can't natively combine two NAS devices and make them appear as a logical storage unit. However, third-party products, such as 1Vision Software's vNAS, let you configure multiple WPNAS devices as a single storage pool. Such virtualization of NAS allows for logical-unit—like configuration and provides for more sophisticated NAS solutions. For example, vNAS, which is loaded on each WPNAS device in a storage pool, lets an administrator set up a storage threshold rule such as "When I reach 75 percent capacity, start storing files on another WPNAS device in the storage pool."

As the cost of storage drops below one cent per megabyte, disk-based backup is becoming an increasingly viable alternative to tape storage. The benefits of disk storage are easier backup management and instant restores. Disk storage lets you keep all your essential files in nearline storage and makes them available within seconds to quick-restore applications. Today, a request such as "Can you restore those five messages I deleted about a month ago?" causes a panic. With granular, nearline disk-based backup, you'll be able to restore the messages before you could even find last month's backup tape.

Faster, Cheaper, Better
Over time, I look for all but the smallest organizations to use combined SAN/NAS solutions. Administrators will be able to easily consolidate both file and application server data and have one methodology for storing most of their company's data. For scenarios in which a SAN/NAS fusion box doesn't make sense, NAS devices will meet the need. Networked storage solutions provide the basis of a state-of-the-art Windows infrastructure, providing an impressive Return on Investment (ROI) and making IT administrators' jobs easier.