Even in this prolonged economic downturn, storage capacity continues to grow. In fact, a recent study by the Meta Group projects a 90 percent annual growth rate over the next two years. Faced with this challenge, consolidation has emerged as the Holy Grail for enterprise storage managers. It is the key to gaining control over the continuously expanding storage capacity while reigning in the rapidly escalating cost of managing storage. Declares John McArthur, Group vice president, Worldwide Storage Research at International Data Corp. (LDC), Framingham, Mass.: "Our research confirms that storage consolidation provides real operational benefits and delivers real savings."
Simply put, storage consolidation enables administrators to reduce the number of storage systems needed to support data center applications, lowering costs across the board. For example, reducing the number of storage systems in a data center frees up floor space and lowers operating expenses because the power and air conditioning requirements of the data center decrease. The real payoff, however, comes from the reduced complexity--fewer systems to be managed with corresponding increase in administrator productivity--as well as increased storage utilization and a reduction in software and maintenance costs.
Meeting the Capacity Challenge: Consolidation and SANs The first phase of storage consolidation was the relocation of storage back to the data center. Storage that had moved out of the data center with the introduction of low cost open systems servers is now migrating back as the costs of managing the growth of storage increases. Storage Area Networks (SANs) have provided the connectivity to enable large-scale consolidation around sharable pools of storage. Logical units (LUNs) of storage can be reallocated among servers from these easily expandable pools of storage through SAN management tools without the need to physically re-cable the storage devices. No longer does one server run out of storage without being able to tap excess storage on another server. SANs, in effect, allow enterprises to stay ahead of the ever-expanding need for storage capacity without worrying about how much storage each server will need when.
Beyond sheer storage capacity, enterprises are facing an even higher growth in transaction rates against that data As more businesses expand their markets and provide services online, the volume of transactions against a given amount of storage is increasing dramatically. Front office applications such as retail point-of-sale, web serving, funds transfers, online banking, airline reservations, and others, drive a host of back office application transactions. The need for real-time billing cycles, supply chain management, and CRM further increase the transaction load.
This growth in transaction rates complicates storage consolidation. An increase in transaction rates requires an increase in servers. As more transaction servers are brought on line, they need additional connectivity and bandwidth to the same storage source. Many older storage systems have had to add storage controllers to satisfy this demand for connectivity and bandwidth, even though they are using only a fraction of their maximum storage capacity. In addition to the cost of another controller, applications may need to be split into multiple instances, data may need to be duplicated; and additional software licenses are required. Adding controllers negates many of the benefits of storage consolidation.
Meeting the Bandwidth Challenge: Virtual Private Storage
As more and more servers were connected to the storage network, the number of physical ports available in a storage system also became a concern. Customers began asking for an increase in storage ports from 16 to 32 to 64, which would have added a great deal of cost and left underutilized port bandwidth on the table. While most Fibre Channel ports today have a bandwidth of 200MB/s, most applications are only transferring at 5 or 10MB/s. This will become an even bigger gap when the industry moves to 10GB/s speeds.
One possible solution was to connect many servers through the same storage port, but users were reluctant to do so since the servers all have to share the same set of LUN addresses. Only one server could use LUN 0 for system boot, and all the other LUN addresses had to be carefully partitioned between the servers in order to avoid corruption of each other's data.
Hitachi responded by virtualizing the storage ports so that each physical port looked like 128 virtual ports. Unlike physical ports that require a mode set to communicate with different host platforms and thus can handle only one flavor of host, virtual ports can support many heterogeneous open systems platforms simultaneously (see figure).
This works because each virtual port can be assigned its own virtual private storage space so that multiple heterogeneous hosts that share the same physical port no longer need to share the same LUN address space. They can reboot independently through their own LUN 0 and there is no danger of overwriting each other's data. This ensures safe multi-tenancy; that is, multiple heterogeneous hosts can safely share a common physical storage system. Virtual private storage is analogous to virtual private networks in the IF networking world.
