HP B6960-96035, Concepts Manual

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4. The BSM starts Disk Agents (DAs) for each disk to be backed up in parallel. The
actual number of Disk Agents started depends on the concurrency of Disk Agents
configured in the backup specification. This is the number of Disk Agents that
can be started to send data in parallel to a Media Agent, thus allowing a device
to stream.
5. Disk Agents read data from disks and send it to the Media Agents that write
data to media.
In a backup session with object mirroring, Media Agents used for writing mirrored
objects are daisy-chained. Each Media Agent writes the received data to media
and forwards it to the next Media Agent in the chain.
6. The BSM monitors the progress of the session and starts new Disk Agents and
new Media Agents as necessary.
7. When the backup session is completed, the BSM closes the session.
Figure 63 Backup session information flow (1)
How many sessions can run concurrently?
A number of backup sessions can run in the cell at the same time. This number is
limited by resources in the cell, such as the availability of devices and the configuration
of the Cell Manager, for instance, processor speed, main memory size, and similar.
How Data Protector operates 222