A.3. On-line changes to network communications

A.3.1. Changing the replication protocol

Prior to DRBD 8.4, changes to the replication protocol were impossible while the resource was on-line and active. You would have to change the protocol option in your resource configuration file, then issue drbdadm disconnect and finally drbdadm connect on both nodes.

In DRBD 8.4, the replication protocol can be changed on the fly. You may, for example, temporarily switch a connection to asynchronous replication from its normal, synchronous replication mode.

Changing replication protocol while connection is established. 

drbdadm net-options --protocol=A <resource>

A.3.2. Changing from single-Primary to dual-Primary replication

Prior to DRBD 8.4, it was impossible to switch between single-Primary to dual-Primary or back while the resource was on-line and active. You would have to change the allow-two-primaries option in your resource configuration file, then issue drbdadm disconnect and finally drbdadm connect on both nodes.

In DRBD 8.4, it is possible to switch modes on-line.

[Caution]Caution

It is required for an application using DRBD dual-Primary mode to use a clustered file system or some other distributed locking mechanism. This applies regardless of whether dual-Primary mode is enabled on a temporary or permanent basis.

Refer to Section 6.8.2, “Temporary dual-primary mode” for switching to dual-Primary mode while the resource is on-line.