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Storage Utilization
Effective use of storage devices differentiates between installed capacities, allocated and used capacity, allocated and unused capacity, and free or unallocated space. These measurements provide valuable insight into building a more cost-effective storage infrastructure. Industry average storage utilization figures differ by operating system and by the type of storage devices. Mainframe systems have higher allocation and utilization levels as a result of the powerful suite of proven storage management tools. Non-mainframe systems don't have the equivalent suite of mainframe-class tools to enable high levels of utilization making higher utilization a more labor intensive process.
For non-mainframe disk systems, the allocated/used levels for a physical disk average about 40 percent. The mainframe disk allocated/used levels are typically double that of non-mainframe systems and average about 80 percent. Remember, these are averages. The challenges for disk utilization levels on both mainframe and non-mainframe systems are growing as the capacity of new disk drives is increasing much faster than drive performance. Today's largest disk drive capacity is 500 gigabytes. Increasing disk capacity without a corresponding increase in disk performance normally creates throughput bottlenecks as contention for the single actuator increases. As a result, storage administrators often deliberately allocate less space on higher-capacity disk drives in order to maintain acceptable performance levels. This ultimately increases disk costs as actual utilization levels drop. A few new disk drive startup and early stage companies are aiming for better disk utilization and performance levels by adding policy-based intelligence to create "bands" for varying levels of performance on the disk.
Tape cartridge utilization also varies by operating system and by tape architecture. For mainframe systems, tape cartridge allocated/used levels were often 25 percent or less before the arrival of virtual tape library systems in 1997. Virtual tape libraries enabled intelligent stacking of multiple logical tape volumes on a single tape cartridge proving to be highly effective in driving up cartridge utilization. Virtual tape library users now experience allocated/used levels for tape cartridges of 80 percent or more. This becomes more important as the capacity of a tape cartridge now exceeds the capacity of a disk drive. With compression, tape cartridges can exceed one terabyte in capacity.
Non-mainframe tape systems traditionally had very high allocated/used levels for tape cartridges since the only application that used tape was backup/recovery. When tape cartridge capacities were smaller than disk drive capacities, then backup process would often fill one or more cartridges. Tape capacities surpassed disk drive capacities in the 2001 timeframe and today a tape cartridge can hold the contents of several disk drives. In addition, more backup and replication applications operate on smaller files or sub-files rather than a full disk volume making the amount of data written on tape significantly less than the cartridge capacity. The result is that non-mainframe tape allocated/used percentages are experiencing efficiency problems and are routinely below 50 percent, similar to mainframe utilization figures prior to virtual tape libraries.
Effective storage utilization has become tough to attain in past years and increasing utilization without the likelihood of decreasing performance can be difficult. Improving storage utilization reduces the storage infrastructure/hardware costs since more efficient hardware usage decreases unnecessary hardware consumption. As the size of the storage environment increases, this challenge increases. Storage Utilization - How Efficient Is Your Storage?
Source: Horison Information Strategies: Storage Navigator
© 2005 Horison
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