How to configure GlusterFS server quorum

Network partitions in a GlusterFS trusted pool can leave servers making management decisions from partial cluster membership. Server quorum makes glusterd require the configured percentage of pool members before participating volumes continue serving from that side of the partition.

Two settings are involved. cluster.server-quorum-ratio is a trusted-pool setting and is applied with gluster volume set all, while cluster.server-quorum-type is set on each volume that should participate. When quorum is lost on a node, glusterd can bring down brick processes for participating volumes until enough pool members are reachable again.

Server quorum protects server-side volume configuration and brick process state, not the client I/O path by itself. On a two-node trusted pool, any ratio above 50 percent requires both nodes to remain online, so use a three-node, arbiter, or otherwise documented design when failover during one server outage is required.

1. Check trusted-pool connectivity from a GlusterFS server.

   $ sudo gluster peer status
   Number of Peers: 2
   
   Hostname: node2
   Uuid: 22222222-3333-4444-5555-666666666666
   State: Peer in Cluster (Connected)
   
   Hostname: node3
   Uuid: 33333333-4444-5555-6666-777777777777
   State: Peer in Cluster (Connected)

   Related: How to create a GlusterFS trusted storage pool

2. Check the target volume before changing quorum participation.

   $ sudo gluster volume info volume1
   
   Volume Name: volume1
   Type: Replicate
   Status: Started
   Number of Bricks: 1 x 3 = 3
   Transport-type: tcp
   Bricks:
   Brick1: node1:/bricks/volume1/brick
   Brick2: node2:/bricks/volume1/brick
   Brick3: node3:/bricks/volume1/brick

   Replace volume1 with the volume that should participate in server-side quorum.

3. Set the trusted-pool server quorum ratio.

   $ sudo gluster volume set all cluster.server-quorum-ratio 51%
   volume set: success

4. Enable server quorum participation on the volume.

   $ sudo gluster volume set volume1 cluster.server-quorum-type server
   volume set: success

   On a two-node trusted pool, a ratio above 50 percent means both servers must stay connected. A dummy peer without bricks does not make replica-2 client writes safe from split-brain.

5. Verify the saved server quorum options.

   $ sudo gluster volume info volume1
   
   Volume Name: volume1
   Type: Replicate
   Status: Started
   Number of Bricks: 1 x 3 = 3
   Transport-type: tcp
   Bricks:
   Brick1: node1:/bricks/volume1/brick
   Brick2: node2:/bricks/volume1/brick
   Brick3: node3:/bricks/volume1/brick
   Options Reconfigured:
   cluster.server-quorum-type: server
   cluster.server-quorum-ratio: 51%

6. Check brick process state after the change.

   $ sudo gluster volume status volume1
   Status of volume: volume1
   Gluster process                             TCP Port  RDMA Port  Online  Pid
   ------------------------------------------------------------------------------
   Brick node1:/bricks/volume1/brick           49152     0          Y       1844
   Brick node2:/bricks/volume1/brick           49153     0          Y       1901
   Brick node3:/bricks/volume1/brick           49154     0          Y       1968
   
   Task Status of Volume volume1
   ------------------------------------------------------------------------------
   There are no active volume tasks

   Online: Y on each brick confirms the volume is still serving while quorum is met. Test partition behavior only in a lab or a planned maintenance window.
   Related: How to check GlusterFS volume status