SAN Appliances Ease SAN Implementation.

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.

Boot from SAN provides the capability to boot Windows NT or Windows 2000 servers from a Fibre Channel disk array in the SAN. In case of a server failure, a new server can be brought online by booting from an external SAN disk, which helps bring applications back online quickly because the new server has all the same configuration information as the one it replaced.

Mirroring data locally and remotely enables a more robust disaster recovery environment. This capability is key for a disaster recovery solution that provides quick recovery and access to business critical data--as opposed to disruptive incremental and full tape backup and burdensome recovery times.

Appliance-based Virtualization 

Many major storage analysts and industry experts have acknowledged that virtualization is an essential next-step to truly centralized storage environments. SAN appliance based virtualization is implemented in the fabric of a SAN, with an independent platform managing storage. SAN appliance-based virtualization can support heterogeneous SAN environments, has no server or storage vendor lock-in, and provides consistent cross-platform management and a centralized point of SAN control (Figure 1).

While appliance-based virtualization can potentially add a layer of complexity to a fabric's basic tasks, the ability to centrally administer a broad expanse of storage with the same tools and procedures can reduce administrative costs.

Types Of SAN Appliances

There are two different architectural approaches to a SAN appliance--symmetric and asymmetric (Figure 2). Asymmetric SAN appliances provide an out-of-band storage management platform. The SAN appliance functions outside the data path, that is, it allows data transfers between servers and storage to occur independently. The appliance performs management functions independent of the application servers. Host software and or drivers are required and the placement of the SAN appliance can cause potential server performance issues. Also, administration effort can intensify with each attached server.

Symmetric SAN appliances offer an in-band storage management platform. The SAN appliance functions in the data path, sitting between servers and storage devices in a SAN. Symmetric appliances do not require host or software drivers and can be 'clustered' for high availability. Because symmetric SAN appliances sit in the data path, there is a potential for capacity and throughput issues. Capacity issues can be mitigated by adding switches to increase connectivity and by leveraging higher performance processors in the SAN Appliance itself. Throughput issues can be addressed by leveraging higher performance processors in the SAN Appliance, designing SANs with performance optimized zones, and using a more 'optimized' storage OS on the SAN Appliance.

Potential Of SAN Appliances

In addition to reducing storage TCO, easing SAN deployments and providing benefits including centralized management, advanced feature sets, and storage virtualization, SAN appliances provide a roadmap for future interoperability. SAN appliances promote vendor interoperability through a centralized management system that accommodates rapid, data-intensive growth. Customer adoption of SAN appliances is essential to the realization of true SAN interoperability.

Bruce Kornfeld is the director of worldwide marketing in the Storage Systems Group at Dell Computer Corp. (Round Rock, TX).

Focus On Virtualization

The concept of virtualization centers around the ability to disassociate the logical representation of a disk presented to a host system from the physical components that make up the logical disk or LUN. This permits administrators to create logical volumes or virtual disks from actual physical storage. Virtualization also allows administrators to aggregate physical drives and create a virtual pool of storage that can be parceled out to a group of servers. Administrators can add disks to the pool, shift unused capacity from one server to another, and initiate new servers into the pool--all without disrupting the production of established servers. Without virtualization, these tasks would require administrators to shut down storage systems and servers and then reboot in order to initialize the configuration changes.

Since virtualization is such a hot technology right now, it's being implemented in a variety of ways, not solely by SAN appliances.

Server-based virtualization is achieved by software that runs on servers. It can be easy to adopt, but difficult to manage. Since the software is on the servers, this implementation could lead to operating system or Host Bus Adapter vendor lock in and difficult server-to-server data replication.

Storage-based virtualization is often implemented on high-end intelligent disk arrays. This provides a broad storage management feature set, but customers will generally have to pay a premium for the functionality and it only applies to a single vendor's storage. This implementation can encounter capacity and throughput limitations.

The ability to efficiently manage storage capacity, coupled with the flexibility to expand storage on the fly, allows customers to react to and manage the explosive and unpredictable demand for storage. Virtualization can help to reduce management costs because the creation of a storage pool increases the amount of storage one administrator can manage in the same amount of time. Virtualization also preserves investment in storage technologies and offers more choice for future expansion.