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4 Keys To Storage Management: Page 3 of 3

Channels connecting host processors to disk and tape storage devices vary as to their transfer speed, their technology, and the maximum number able to be attached to different platforms. The number and speed of the channels influence performance, response, throughput, and costs. All of these factors should be considered by storage management specialists when designing an infrastructure's channel configurations.

Tape and disk controllers have variable numbers of input channels attaching them to their host processors, as well as variable numbers of devices attaching to their output ports. Analysis needs to be done to determine the correct number of input channels and output devices per controller to maximize performance while still staying within reasonable costs. There are several software analysis tools available to assist in this; often the hardware suppliers can offer the greatest assistance.

A software methodology called a logical volume group assembles together two or more physical disk volumes into one logical grouping for performance reasons. This is most commonly done on huge disk-array units housing large databases or data warehouses. The mapping of physical units into logical groupings is an important task that almost always warrants the assistance of performance specialists from the hardware supplier or other sources.

To improve performance of disk transactions, huge disk arrays also have varying sizes of cache memory. Large database applications benefit most from utilizing a very fast -- and very expensive -- high-speed cache. Because of the expense of the cache, disk-storage specialists endeavor to tune the databases and the applications to make maximum use of the cache. Their goal is to have the most frequently accessed parts of the database residing in the cache. Sophisticated pre-fetch algorithms determine which data is likely to be requested next and then initiate the preloading of it into the cache. The effectiveness of these algorithms greatly influences the speed and performance of the cache. Since the cache is read first for all disk transactions, finding the desired piece of data in the cache -- for example, a hit -- greatly improves response times by eliminating the relatively slow data transfer from physical disks. Hit ratios (hits versus misses) between 85 percent and 95 percent are not uncommon for well-tuned databases and applications; this high hit ratio helps justify the cost of the cache.

Two more recent developments in configuring storage systems for optimal performance are storage area networks (SANs) and network attached storage (NAS). SAN is a configuration enhancement that places a high-speed fiber-optic switch between servers and disk arrays. The two primary advantages are speed and flexibility. NAS is similar in concept to SAN except that the switch in NAS is replaced by a network. This enables data to be shared between storage devices and processors across a network. There is a more detailed discussion on the performance aspects of these two storage configurations described in Chapter 8, "Performance and Tuning."

To read Chapter 12 in full, click here.

Chapter 12: Storage Management is is an excerpt from
IT Systems Management,
by Rich Schiesser, published by Prentice Hall Professional

Infrastructure expert and world acclaimed author Rich Schiesser combines the expertise of a senior IT executive, professional educator, industry spokesman and sought-after consultant to benefit numerous clients in a variety of industries world-wide.