How bandwidth limiting works

When a backup starts, NetBackup reads the bandwidth limit configuration as configured in the Bandwidth host properties. NetBackup then determines the appropriate bandwidth value and passes it to the client. NetBackup computes the bandwidth limit that is based on the current set of active backups on the subnet and the new backup that starts. Backups that start later are not considered. NetBackup does not include local backups in its calculations.

The NetBackup client software enforces the bandwidth limit. Before a buffer is written to the network, client software calculates the current value for kilobytes per second and adjusts its transfer rate if necessary.

As the number of active backups increase or decrease on a subnet, NetBackup dynamically adjusts the bandwidth limits on that subnet. If additional backups are started, the NetBackup server instructs the other NetBackup clients that run on that subnet to decrease their bandwidth setting. Similarly, bandwidth per client is increased if the number of clients decreases. Changes to the bandwidth value occur on a periodic basis rather than as backups stop and start. The periodic changes reduce the number of bandwidth value changes that are required.