When protecting DataKeeper volume resources in Microsoft WSFC, if all nodes are included in the cluster split-brain recovery should occur automatically.
However, in a Node Outside the Cluster scenario a split-brain may occur if network connectivity is lost to the DR Node. The user might choose to manually switchover the volume to the DR node while WSFC maintains the source on the original cluster node. When network connectivity to the DR node is restored there will be a conflict known as a split-brain condition where both systems assume the ownership role over the volume. The SIOS DataKeeper user interface will display the error “Mirror Inconsistencies – Click the following mirror(s) to resolve source conflicts – Mirroring is halted until this is resolved” (as shown in the diagram below).
In addition, the following error is logged to the System Event log:
An invalid attempt to establish a mirror occurred. Both systems were found to be Source.t
Local Volume: F
Remote system: 192.168.1.212
Remote Volume: F
The mirror has been paused or left in its current non-mirroring state.
Refer to Extending a Clustered DataKeeper Volume to a Node Outside the Cluster for the recovery procedure.
Resolving a Split-Brain Issue via the Command Line Interface
EMCMD <system> PREPARETOBECOMETARGET <volume letter>
This command should only be used to recover from a Split-Brain condition. It should be run on the system where the mirror is to become a target and is only valid on a mirror source. This command causes the mirror to be deleted and the volume to be locked.
To complete split-brain recovery, run CONTINUEMIRROR on the system that remains as the mirror source.
If volume F: is a mirror source on both SYSA and SYSB, you can use emcmd to resolve this split-brain situation. Choose one of the systems to remain a source – for example, SYSA. Make sure there are no files or modifications on SYSB that you want to save – if so, these need to be copied manually to SYSA. To re-establish the mirror, perform the following steps:
EMCMD SYSB PREPARETOBECOMETARGET F
The mirror of F: on SYSB will be deleted and the F: drive will be locked.
EMCMD SYSA CONTINUEMIRROR F
Mirroring of the F: drive from SYSA to SYSB will be established, a partial resync will occur (overwriting any changes that had been made on SYSB), and the mirror will reach the Mirroring state.