Proven Disk Performance Solutions

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With optimization appearing to fail to make the grade as an enterprise solution, what, then, are the proven techniques for improving disk performance?

RAID

Hardware RAID has a proven track record in the corporate world, both in terms of performance and robustness. Throughput is increased by handling logically contiguous disk operations in parallel instead of as one longer operation on a single disk. Although the adoption of RAID is widespread in large companies, its lack of use among small to mid-sized companies appears to be related to cost rather than reliability issues. But, if it can be made affordable, RAID represents an excellent way of increasing disk performance. In recent years, the cost equation has improved to where most mid-sized and even some small businesses are now able to take advantage of RAID. So, for better disk performance, hardware RAID is a good direction to go. Most companies that are looking for higher performance I/O go straight to RAID and are not overly concerned with disk optimization and data layout on the drive. NSTL notes, however, that RAID is just as susceptible to fragmentation as other disk configurations. According to NSTL, a fragmented file would not incur an I/O cost only if the file fragments happened to be in the same data stripe, which may not be likely. Usually, however, the effect of fragmentation on RAID is the same as on a non-RAID system: Additional head movement and I/O will be necessary in order to perform file operations. A safe and reliable network disk defragmenter, then, should be used regularly to keep RAID systems functioning optimally.

Caching

Caching is based on the principle that data that has been read or written is likely to be read again. Because memory access is many times faster than disk access, the caching of recently used files can significantly reduce I/O traffic. As a result, caching aids performance even in heavily fragmented systems. When NSTL tested the impact of fragmentation on a well-cached system, however, it still found that as little as 13 percent disk fragmentation exacted a definite toll on performance; thus, disk caching mitigates but does not eliminate these problems. Unless instructed otherwise, NT's Cache Manager caches all reads and writes on all secondary media. Cache Manager uses a number of aggressive techniques to improve performance. For example, it will attempt to read ahead in a file in anticipation of a program's requesting the succeeding data. It will also delay writes to the disk, so that if reads or writes of the same data occur quickly, they will be satisfied out of the cache rather than through a physical disk operation. Aggressive disk caching can mitigate the effects of disk fragmentation to the extent that data read by applications is read from the cache rather than from the disk itself. In fact, adding memory to a heavily fragmented system can improve performance on a fragmented system, although this is an expensive solution to a problem that can be fixed at little cost through software and good practices.

Defragmentation

Much like the importance of regular oil changes to vehicle maintenance, the tried and tested solution for disk performance problems on Windows NT and Windows 2000 is regular defragmentation. Independent performance tests by NSTL have shown conclusively that defragmentation produces significant gains for both workstations and servers (see Chapter 7). With these results comparing favorably with most hardware upgrades, it is no wonder that network defragmenters are becoming the norm in large corporations.



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Server Disk Management in a Windows Enviornment
Server Disk Management in a Windows Enviornment
ISBN: N/A
EAN: N/A
Year: 2003
Pages: 197

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