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NetBackup Storage Device Performance

This section lists some factors to consider when you evaluate the storage device component of the NetBackup data transfer path to identify possible changes that may improve the overall performance of NetBackup.

Tape drive wear and tear is much less, and efficiency is greater if the data stream matches the tape drive capacity and is sustained. Generally speaking, most tape drives have much slower throughput than most disk drives. We recommend using no more than two high performance tape drives per SCSI/FC connection. The SCSI/FC connection should be able to handle both drives at the maximum rated throughput.

These are some of the factors which affect tape drives:

  • Media Positioning. When a backup or restore is performed, the storage device must position the tape so that the data is over the read/write head. Depending on the location of the data and the overall performance of the media device, this can take a significant amount of time. When you conduct performance analysis with media containing multiple images, it is important to account for the time lag that occurs before the data transfer starts.

  • Tape Streaming. If a tape device is being used at its most efficient speed, it is said to be streaming the data onto the tape. Generally speaking, if a tape device is streaming, there will be little physical stopping and starting of the media. Instead the media will be constantly spinning within the tape drive. If the tape device is not being used at its most efficient speed, it may continually start and stop the media from spinning. This behavior is the opposite of tape streaming and usually results in a poor data throughput rate.

  • Data Compression. Most tape devices support some form of data compression within the tape device itself. Highly compressible data will yield a higher data throughput rate than incompressible data if the tape device supports hardware data compression. This will be true even if the tape device is able to stream the data onto the tape for both the highly compressible data and the incompressible data.

Tape devices typically come with two performance values: Maximum Throughput Rate and Nominal Throughput Rate. The maximum throughput rate is based on how fast compressible data can be written to the tape drive when hardware compression is enabled. The nominal throughput rates applies to less than ideal conditions.

In general, if your hardware device supports compression, you may not want to use software compression such as that available in NetBackup. If you do so, in some cases the size of the data as stored on the media may actually increase because the data has gone through more than one compression algorithm. However, there may still be other valid reasons to use the software compression in NetBackup, such as reducing the amount of data that must be transmitted across the network for a remote client backup.



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Implementing Backup and Recovery(c) The Readiness Guide for the Enterprise
Implementing Backup and Recovery: The Readiness Guide for the Enterprise
ISBN: 0471227145
EAN: 2147483647
Year: 2005
Pages: 176

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