NetBackup storage device performance in the data transfer path
This section looks at storage device functionality in the NetBackup data transfer path. Changes in these areas may improve NetBackup performance.
Tape drive wear and tear is much less, and efficiency is greater, if the data stream matches the tape drive capacity and is sustained. Most tape drives have slower throughput than disk drives. Match the number of drives and the throughput per drive to the speed of the SCSI/FC connection, and follow the hardware vendors' recommendations.
The following factors affect tape drives:
When a backup or restore is performed, the storage device must position the tape so that the data is over the read and write head. The positioning can take a significant amount of time. When you conduct performance analysis with media that contains multiple images, allow for the time lag that occurs before the data transfer starts.
SCSI bus assignment
Connect the tape drives to different SCSI buses. For example: If you have 8 tape drives, use a minimum of 4 SCSI cards and connect no more than 2 drives to each card.
If a tape device is used at its most efficient speed, it is "streaming" the data onto the tape. If a tape device is streaming, the media rarely has to stop and restart. Instead, the media constantly spins within the tape drive. If the tape device is not 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.
Most tape devices support some form of data compression within the tape device itself. Compressible data (such as text files) yields a higher data throughput rate than non-compressible data, if the tape device supports hardware data compression.
Tape devices typically come with two performance rates: maximum throughput and nominal throughput. Maximum throughput is based on how fast compressible data can be written to the tape drive when hardware compression is enabled in the drive. Nominal throughput refers to rates achievable with non-compressible data.
Note:
NetBackup cannot set tape drive data compression. Follow the instructions that are provided with your OS and tape drive.
In general, tape drive data compression is preferable to client (software) compression. Client compression may be desirable for reducing the amount of data that is transmitted across the network for a remote client backup.
More Information