HP Data Protector Software Performance White Paper

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Figure 55. CPU load of HP-UX local backup to Ultrium 960 with segment sizes 10 – 10,000 MB
Note: Larger segments sizes improve the backup performance but could have negative impact
on restore performance. Data blocks are found faster if restored from a backup with smaller
segment sizes.
Disk Agent buffers
Data Protector Media Agents and Disk Agents use memory buffers to hold data waiting to be
transferred. This memory is divided into a number of buffer areas (one for each Disk Agent and
depending on device concurrency). Each buffer area consists of eight Disk Agent buffers (of the
same size as the block size configured for the device).
This value can be changed while configuring a new device or when changing the device
properties using the advanced options for the device, although this is rarely necessary. There
are two basic reasons for changing this setting:
1. Shortage of memory
If there is a shortage of memory, the shared memory required for a Media Agent can be
calculated as follows:
Media Agent Shared Memory = Disk Agent Concurrency x Number of Buffers x Block Size
2. Streaming
If the available network bandwidth varies significantly during backup, it is important that a
Media Agent has enough data ready for writing to keep the device in the streaming mode. In
this case, increasing the number of buffers could help.
Figures 56 and 57 demonstrate that different numbers of Disk Agent buffers had no significant
impact on performance in this local backup scenario. The Media Agent always had enough data
ready for writing.
Segment Size 10 - 10.000 MB
CPU Load of HP-UX Local Backup to Ultrium 960
16%
17%
17%
3%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
10 100 1,000 10,000
Segment Size (MB)
CPU Load