Storage Management Strategies for the CIO
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Stop the tape
Despite the attractiveness of disk, organizations with sizeable quantities of data still depend on tape. New generations of tape technology are appearing more frequently but, ironically, the speed and capacity increases aren't always good news. Replacing older technology with new high-performance drives raises expectations of dramatic improvements. In practice, the opposite is often the case.
Tape is a serial technology, so it needs a steady stream of data to maintain its performance. If the data stream can't keep up, performance drops dramatically as the tape drive stops, waits for data, backs up, writes, stops again, etc. This shoe-shining effect also reduces tape drive and media life.
Often, performance problems attributed to "slow tape drives" are actually caused by bottlenecks elsewhere in the data path, and introducing even faster drives actually exacerbates the problem. To improve performance, more data has to be written to fewer drives; for most backup apps this means increasing multiplexing settings.
Does this make multiplexing a best practice? No. Multiplexing is a tradeoff--it may improve backup time, but it degrades restore time. Multiplexing may be a "necessary" practice to deal with the limitations of a given technology in a particular environment, but it's not the preferred way to deal with the problem. A preferred approach is to identify and analyze performance bottlenecks, and to address them where possible. If needed,
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disk may be introduced as a staging device to keep tape streaming, but data from multiple sources doesn't need to be interleaved via multiplexing.
This was first published in September 2006
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