SAN Appliances Ease SAN Implementation - Technology Information

Computer Technology Review, May, 2001 by Bruce Kornfeld

Storage Area Networks have long been the buzz of the IT industry--with promises to provide server and storage consolidation, high availability, speedier backups, and centralized storage management. But the potential complexities and interoperability issues involved in implementing a SAN have been a bit of a buzz killer. A recent addition to the SAN arena is the SAN appliance--a combination of hardware and software designed to ease some of the inherent complexities involved in SAN implementations. Many storage vendors have announced SAN appliance additions to their product lines--some, like Dell, have been shipping SAN appliances for nearly a year. While initial customer reaction has been positive, the majority of businesses still need to understand the inherent benefits that SAN appliances can bring to their organizations.

Why are customers adopting SAN appliances? How do businesses make sense of the different implementations? What does the future hold for this newly heralded storage solution?

Why SAN Appliances?

Customers are turning to SAN appliances to help reduce their storage TCO by easing SAN deployments, providing true centralized management, increasing security, offering advanced storage applications, and providing storage virtualization-all key drivers behind many SAN appliance purchases.

Ease of SAN Deployment

An appliance is generally defined as an intelligent hardware device with bundled software that is designed to perform a well-defined function while hiding the complexity of the underlying software. Of course, the advent of a SAN appliance hasn't immediately lessened the complexity of storage networking technology. But by combining hardware and software into a pre-configured solution and pre-installing advanced SAN software, SAN appliances can lower configuration costs as well as reduce the time to deployment for a fully featured SAN.

True Centralized Management One of the long-promised benefits of SANs has been centralized management. But many storage vendors provide SAN technology that embeds management functions throughout the nodes on a SAN. This distributed management approach leaves customers locked into one storage vendor since management code is tightly linked to the array controller. Also, since this management structure distributes intelligence throughout the SAN, the management environment increases in complexity as customers attempt to scale their SANs to meet the ever-growing data storage requirements. As nodes are added to the SAN, intelligence becomes more distributed and the environment has the potential to become unwieldy to manage, requiring IT departments to hire additional highly trained IT staff, a scarce and expensive resource.

Appliance-based SAN solutions simplify the management structure by centralizing intelligence within the appliance rather than distributing it throughout the SAN. This allows storage administrators to maintain a simple management structure, as well as leverage multiple hosts and storage arrays. SAN appliances can be a cost-effective way to scale storage environments to meet a company's growing data needs, while keeping staffing requirements to a minimum.

Increased Security

SAN appliances can provide secure LUN (Logical Unit Number) masking, enabling administrators to determine which servers in a SAN are exposed and have access to a particular LUN. LUN masking allows administrators to allocate LUNs to specific servers. Traditionally LUN masking has been provided by Host Bus Adapters or server software. However, with a SAN appliance performing this function, businesses can benefit from advanced security because the appliance owns the LUN presentation to the servers. This means that a server added to the SAN cannot access a LUN and subsequently another host's data that it does not have permission to access. Each host only sees what the appliance allows it to see, preventing 'rogue' servers from stepping on other servers' data, which is an added level of security built into the SAN Appliance.

Advanced Storage Applications The SAN appliance can be an ideal platform for advanced storage management applications. Since this advanced functionality is provided by the SAN appliance, customers often don't have to pay licensing fees for software that runs on individual servers or storage arrays, or deal with different implementations among platforms or array vendors. Enterprise-class SAN appliances offer advanced functionality including snapshot copy capabilities, three-way mirroring, boot from SAN, and remote mirroring.

Snapshots create a copy of the block location data of a dataset. Compared to a full copy of a data set, the block location data is a small fraction of the overall volume so the copy process is almost instantaneous. Snapshots are generally used for read-only offline chores--principally backup. Administrators also use snapshots to enhance disaster recovery by generating a copy of data in a known state that can be rolled back to if necessary.

Three-way mirroring generates two mirrors of a dataset in tandem. One of the mirrors can then be taken offline while two-way mirroring continues. Unlike snapshots, this data is not read-only and can be used for a variety of offline chores that require write processing. Typical uses include backup, data warehouse loading, or application testing, with little or no impact on the production data.