HP Data Protector Software Performance White Paper

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stored in data blocks of data segments. Information about each data segment is stored in the
corresponding catalog segment. This information is first stored in the Media Agent memory and
then written to a catalog segment on the medium as well as to the IDB.
All segments are divided by file marks as shown in Figure 53.
Figure 53. Data Protector Medium – data segments, catalog segment, header segment, and file marks
Segment size, measured in megabytes, is the maximum size of data segments. If you back up a
large number of small files, the actual segment size can be limited by the maximum size of
catalog segments. Segment size is user configurable for each device and influences the restore
performance. You can adjust the segment size when configuring a new device or when
changing the device properties using the Advanced options for the device.
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 could be reached faster, which could result in
smaller segment sizes.