Caching is solid with disk option: solid-state, disk-based cache can improve the performance of sluggish networks - Storage

Communications News, Dec, 2003 by Woody Hutsell, Aaron Martz

Storage is a leading cause of under-utilized network resources, under-utilized processors and dissatisfied end-users. The problem can, however, be addressed with a storage cache device using solid-state disk technology. Solid-state, disk-based cache can improve the performance of standard storage and extend the useful life of existing storage deployments, even in SAN environments.

Caching is critical in boosting storage performance, where enterprises need to match their application performance requirements with their storage-access capabilities. Typically, enterprises have relied on the limited caching capability of a RAID controller or high-performance internal cache capabilities available only in high-end storage systems. An external solid-state disk cache can provide advantages beyond these traditional "built-in" caches.

Superior performance. External solid-state cache from a quality manufacturer should provide hundreds of thousands of I/Os per second and thousands of MB per second in bandwidth.

Scalability. Internal cache locks a datacenter into a finite maximum capacity. External solid-state cache units typically have superior capacity densities and, when one unit is full, additional units can be seamlessly added for even more performance and capacity.

Broader use. Typical storage cache is restricted to use with that storage subsystem, but an external solid-state cache can be attached to multiple storage devices simultaneously. A single solid-state disk cache may be leveraged across the entire networked storage infrastructure.

Maximum flexibility. Over time, an external cache can be moved to accelerate a storage environment, maximizing its potential contribution. Since it is not tied to the proprietary systems of a specific storage manufacturer, solid-state disk caches typically have a superior array of configuration options.

Cost effectiveness. Solid-state disk cache can offer savings through delaying or avoiding expensive forklift upgrades and data migration by accelerating existing storage and extending its useful life.

When choosing a solid-state disk-cache solution, the user has two choices-file level or block level caching. File caching, the more traditional method, involves a solid-state disk that looks just like any other storage device to the network. It is a drive letter where data can be written and read like any other drive, only faster.

This is a possible solution for dealing with static network "hot files" that constantly undergo activity. It is also useful for accelerating applications constrained by a particular operation. For example, a Sybase database can experience dramatic acceleration by assigning its temporary workspace (tempdb) to a file-caching solid-state disk.

The alternative method is block-level caching, where the solid-state disk caches data automatically and invisibly (at the block level). To the network, the cached storage devices are simply running faster, and the solid-state disk is not "seen" in the path. Block-level caching can be configured to optimize performance in write-or read-intensive environments. This is useful when data on an entire storage system is in high demand or when the amount of hot data exceeds the capacities of solid-state disk units. If access is spread out among the data, a single block cache can make an entire storage system as fast as a solid-state disk.

Applications and data volumes continue to grow, and most enterprises face tough choices as they expand storage environments: technical challenges associated with data migration, matching capacity and performance requirements, and forklift upgrades. The ability to independently scale storage performance can alleviate the pain, and adding solid-state cache devices to the storage network achieves this. Using a solid-state disk can enable an enterprise to extend the useful life of its existing RAID storage.

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Woody Hutsell is executive vice president and Aaron Martz heads up communications for Texas Memory Systems, Houston.