Overview

This document explains TAC Split brain and Split brain Solution.

Method

1. TAC network and storage configuration

1) TAC network

2) TAC storage

2. TAC Split brain

1) TAC Split brain CASE

- Each node determines that the other node is down and stops sending BLOCK/LOCK information. 

- Each node operates under the assumption that the other is dead, and if the same BLOCK on the shared disk is modified during operation, data inconsistency and corruption may occur.

2) TAC Split brain Solution

• Election

  

  - All nodes write a FILE H/B message to the CMFILE every second.

  - The MASTER node writes a FILE H/B message to the CMFILE every second and checks the FILE H/B messages from the SLAVE nodes.

  - When the NET H/B expires, the MASTER node determines which nodes to shut down and which to keep alive, and writes an Alive message to the CMFILE.

  - Each node checks its own Alive message in the CMFILE to determine whether it should shut down or remain active.

  - If the MASTER node goes down, the remaining nodes go through the Election process via the CMFILE to select a new MASTER node.

• Master Selection

  - The Master node is determined by the TBCM and Cluster startup order; the first TBCM and Cluster node to start becomes the MASTER node.

   

• Master Change

  1) Condition 

   - This process occurs when the MASTER node is down.

  2) Procedure

   - The MASTER node election favors the node with the lowest TBCM NID value.

   - TBCM NID value - When all TBCMs are stopped, NID values are assigned in the order the Cluster is started.

   - NID 1: MASTER node, and for the rest, the NID increases by 1 in the order they join (connect to) the Cluster.

   - If the MASTER node goes down, the node with the lowest NID among the healthy nodes becomes the MASTER node.

  3) Result 

  - Once the MASTER node is determined, the MASTER node's CM_SID and NID are recorded in the Cluster section of the CMFILE. 

  - Each node reads the CMFILE and learns that the MASTER node has been determined, and the node designated as MASTER changes its status accordingly.

  4) Others 

  - You cannot intentionally designate a specific node as the MASTER node.

  - You cannot change the MASTER node without stopping the Cluster when the MASTER node has already been determined.