Split-Brain Recovery in HA Installation
The split-brain problem is a DRBD synchronization issue (HA status shows DUnknown in the DRBD disk state), which occurs when both HA nodes are rebooted. For example, in cases of electricity shut-down. To recover, please follow the below steps:
Step 1: Manually choose a node where data modifications will be discarded.
It is called the split-brain victim. Choose wisely; all modifications will be lost! When in doubt, run a backup of the victim’s data before you continue.
When running a Pacemaker cluster, you can enable maintenance mode. If the split-brain victim is in the Primary role, bring down all applications using this resource. Now switch the victim to the Secondary role:
victim# drbdadm secondary ha_data
Step 2: Disconnect the resource if it’s in connection state WFConnection:
victim# drbdadm disconnect ha_data
Step 3: Force discard of all modifications on the split-brain victim:
victim# drbdadm -- --discard-my-data connect resource
For DRBD 8.4.x:
victim# drbdadm connect --discard-my-data resource
Step 4: Resync starts automatically if the survivor is in a WFConnection network state. If the split-brain survivor is still in a Standalone connection state, reconnect it:
survivor# drbdadm connect resource
Now the resynchronization from the survivor (SyncSource) to the victim (SyncTarget) starts immediately. There is no full sync initiated, but all modifications on the victim will be overwritten by the survivor’s data, and modifications on the survivor will be applied to the victim.