HP B6960-96035 - Manual (Page 159)

Increasing the block size can improve performance. Changing the block size should
be done before formatting tapes. For example, a tape written with the default block
size cannot be appended to using a different block size.
NOTE:
Use the same block size for media that can be used with different device types. Data
Protector can only append data to media using the same block size.
Number of 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, depending on device concurrency). Each buffer area consists
of 8 Disk Agent buffers (of the same size as the block size configured for the device).
You can change this value to be anything between 1 and 32, although this is rarely
necessary. There are two basic reasons to change this setting:
• Shortage of memory
The shared memory required for a Media Agent can be calculated as follows:
DAConcurrency*NumberOfBuffers*BlockSize
Reducing the number of buffers from 8 to 4, for instance, results in a 50% reduction
in memory consumption, with performance implications.
• Streaming
If the available network bandwidth varies significantly during backup, then it
becomes more important that a Media Agent has enough data ready for writing
to keep the device in the streaming mode. In this case, increase the number of
buffers.
Device locking and lock names
Device names
When configuring devices for use with Data Protector, you can configure the same
physical device many times with different characteristics simply by configuring the
same physical device in Data Protector with different device names. For example, a
simple standalone DDS device can be configured as a compressed device and then
as an uncompressed device, although this is not recommended.
Concepts guide 159