HP Data Protector Software Performance White Paper

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Figure 51 shows that enabling CRC checking required additional CPU resources. The CRC ON
test resulted in more than twice the CPU load.
Figure 51. CPU load of HP-UX local backup to Ultrium 960 with CRC checking OFF/ON
Block size
Segments are not written as whole units, but in smaller subunits called blocks. Data Protector
uses a default device block size regarding different device types. The block size applies to all
devices created by Data Protector and to Media Agents running on the different platforms.
Increasing the block size can improve performance. You can adjust the size when configuring a
new device or when changing the device properties using the Advanced options for the device.
A restore automatically adjusts the block size.
For the Ultrium 960, the block size was configured with a fixed value of 256 KB as shown in
Figure 52 and as described in the section Data Protector configuration on page 37
.
Figure 52. Ultrium 960 Configuration – block size, segment size and disk agent buffers
Segment size
A medium is divided into data segments, catalog segments, and a header segment. Header
information is stored in the header segment, which is the same size as the block size. Data is
Data Protector CRC Check OFF/ON
CPU Load of HP-UX Local Backup to Ultrium 960
37%
16%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
OFF ON
CRC Check
CPU Load