How to create a replicated GlusterFS volume

Replicated GlusterFS volumes keep data available during planned maintenance and help survive an unexpected brick or node outage by storing multiple copies of every file.

A replica volume is built from bricks (directories exported by glusterd) grouped into replica sets. Each write is committed to every brick in the set, while reads can be served from a healthy brick and background self-heal reconciles differences after failures.

Replication trades capacity and write throughput for availability: usable space is roughly raw brick space divided by the replica count. Place replica bricks on separate nodes and on dedicated filesystems (commonly XFS), and avoid using force unless the reduced fault tolerance is acceptable. Replica 3 (or an arbiter design) is commonly chosen over replica 2 when split-brain risk matters.

1. Confirm the trusted storage pool is configured.

   $ sudo gluster peer status
   Number of Peers: 1
   
   Hostname: node2
   Uuid: 0f8b8d42-8d5f-4d19-9a1f-2c1d4d7b9b10
   State: Peer in Cluster (Connected)

   Related: How to set up a trusted storage pool for GlusterFS

2. Create an empty brick directory on each replica node.

   $ sudo mkdir -p /srv/gluster/brick1

   Place brick paths on a dedicated filesystem (not the system root filesystem). Keep the brick directory empty, or volume creation can fail or require force.

   Related: How to mount disks and partitions in Linux

3. Create the replicated volume using a brick count that is a multiple of the replica count.

   $ sudo gluster volume create volume1 replica 2 transport tcp node1:/srv/gluster/brick1 node2:/srv/gluster/brick1
   volume create: volume1: success: please start the volume to access data

   For replica 2, exactly two bricks are required for a single replica set. Add bricks in pairs to expand capacity.

4. Start the new volume.

   $ sudo gluster volume start volume1
   volume start: volume1: success

5. Verify the replica layout from the volume information.

   $ sudo gluster volume info volume1
   Volume Name: volume1
   Type: Replicate
   Volume ID: 7f0c3f1c-2f6b-4d3b-9a3a-2d2c7e5d9e41
   Status: Started
   Snapshot Count: 0
   Number of Bricks: 1 x 2 = 2
   Transport-type: tcp
   Bricks:
   Brick1: node1:/srv/gluster/brick1
   Brick2: node2:/srv/gluster/brick1

6. Verify all bricks are online.

   $ sudo gluster volume status volume1
   Status of volume: volume1
   Gluster process                             TCP Port  RDMA Port  Online  Pid
   ------------------------------------------------------------------------------
   Brick node1:/srv/gluster/brick1             49152     0          Y       2148
   Brick node2:/srv/gluster/brick1             49153     0          Y       1987
   Self-heal Daemon on node1                    N/A       N/A        Y       1763
   
   Task Status of Volume volume1
   ------------------------------------------------------------------------------
   There are no active volume tasks