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Backup
Using Backup Options
Chapter 5234
• Objects that reside on the client connected to the backup device have
a higher priority.
• Objects are selected so that the number of Disk Agents per client is
kept as low as possible.
The size of objects does not play a role in assigning an object to a device.
If a device becomes unavailable, the following happens:
• All objects backed up to the device before the failure time are actually
backed up.
• All objects that are being backed up to the device at failure time are
aborted.
• All objects pending to be backed up to the device will be backed up to
some other available device specified in the backup specification, if
the maximum number of devices has not been used.
Example 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.
The following rules should be considered when applying device options
from a template:
• If the load balancing option is not selected in the template, the device
options are not used with the backup specification.
• If the load balancing option is selected in both the template and the
backup specification, the device options are applied.