Backup

Using Backup Options

• 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.

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Chapter 5