When operating two syslog-ng Store Box (SSB) units in High Availability mode, every incoming data copied from the master (active) node to the slave (passive) node. Since synchronizing data can take up significant system-resources, the maximal speed of the synchronization is limited, by default, to 10 Mbps. However, this means that synchronizing large amount of data can take very long time, so it is useful to increase the synchronization speed in certain situations — for example, when synchronizing the disks after converting a single node to a high availability cluster.

The Basic Settings > High Availability > DRBD status field indicates whether the latest data (including SSB configuration, log files, and so on) is available on both SSB nodes. For a description of each possible status, see Understanding SSB cluster statuses.

To change the limit of the DRBD synchronization rate, navigate to Basic Settings > High Availability, select DRBD sync rate limit, and select the desired value.

Set the sync rate carefully. A high value is not recommended if the load of SSB is very high, as increasing the resources used by the synchronization process may degrade the general performance of SSB. On the other hand, the HA link's speed must exceed the speed of the incoming logs, else the web UI might become unresponsive and data loss can occur.

If you experience bursts of high activity, consider turning on asynchronous data replication.