HP B6960-96035 manual Device streaming and concurrency, How load balancing works

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