How Load Balancing Works; Device Streaming And Concurrency - HP B6960-96035 Concepts Manual

gets full, the backup automatically continues on the medium in the next device in the
device chain.

How load balancing works

For example, assume that there are 100 objects configured for backup to four devices
with concurrency set to three and with load balancing parameters MIN and MAX both
configured at two. If at least two devices are available, the session will start with
three objects being backed up in parallel to each of the first two available devices.
The other 94 objects will be pending and will not be assigned to a particular device
at that time.
Once a backup of a particular object is done, the next pending object is started and
assigned to the device that has less than three concurrent objects being backed up.
Load balancing ensures that the two devices are running in parallel as long as there
are still pending objects to be backed up. If a device fails during backup, one of the
two devices in reserve is used. The objects that were being backed up to the failed
device are aborted, while the next three pending objects are assigned to the new
device. This means that each failure of a device can cause a maximum of three
objects to be aborted, provided that other devices are available for the backup
session to continue.

Device streaming and concurrency

What is device streaming?
To maximize a device performance, it must be kept streaming. A device is streaming
if it can feed enough data to the medium to keep the medium moving forward
continuously. Otherwise, the medium tape has to be stopped while the device waits
for more data. In other words, if the rate at which data is written to the tape is less
than or equal to the rate which data can be delivered to the device by the computer
system, then the device is streaming. In network-focused backup infrastructures, this
deserves attention. For local backups, where disks and devices are connected to the
same system, a concurrency of 1 may suffice if your disks are fast enough.
How to configure device streaming
To allow the device to stream, a sufficient amount of data must be sent to the device.
Data Protector accomplishes this by starting multiple Disk Agents for each Media
Agent that writes data to the device.
156 Media management and devices