Configuring and Using Backup Devices

Device Concurrency, Segment Size, and Block Size

Figure 2-14 Device Properties Dialog Box: Concurrency

Changing

Segment size is related to the size of data areas which Data Protector

Segment Size

uses in writing data to the media. It is user-configurable for each device.

 

Note that a smaller segment size consumes media space because each

 

segment has a file mark which takes up space on a medium. A larger

 

number of file marks results in faster restores, because the Media Agent

 

can quickly locate the segment containing the data to be restored.

 

Optimal segment size depends on the media type used in the device and

 

the kind of data to be backed up. The average number of segments per

 

tape is 50. The default segment size can be calculated by dividing the

 

native capacity of a tape by 50. The maximum catalog size is limited to a

 

fixed number (12 MB) for all media types.

 

Data Protector finishes a segment when the first limit is reached. When

 

backing up a large number of small files, the media catalog limit is

 

reached faster, which can result in smaller segment sizes.

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Chapter 2