GlusterFS Server with Arbiter
When running two GlusterFS servers as a replica, there is a slight chance that a "split brain" situation will occour. To get around this a third GlusterFS server is configured as an arbiter. The arbiter does not have a copy of the data from the other GlusterFS servers, but it has all the metadata. This way the arbiter can help the other servers avoid the "split brain" scenario, without using the diskspace for the data.
In this setup we will configure 2 GlusterFS servers as a replica and 1 as the arbiter.
Network
The GlusterFS servers will have fixed IP-addresses. That is configured in the DHCP servers list of statically assigned IP-adresses by using the Domains MAC address.
- 192.168.1.42 gluster01 (replica)
- 192.168.1.43 gluster02 (replica)
- 192.168.1.44 gluster03 (arbiter)
Disk
Add hardware
To keep things separated the OS will be on one disk and the glusterfs filesystem will be on another disk. For two of the three servers we will add a disk to the domain. This disk will be used for the GlusterFS file storage.
Configure disk
Partition
Create one large partition on /dev/vdb with partition type 8e Linux LVM.
LVM
Set up a new physical volume, configure a volume group.
pvcreate /dev/vdb1 vgcreate vg_data /dev/vdb1
Replica
Add a volume
lvcreate --size 4G --name gluster_home vg_data
Arbiter
Add a volume
lvcreate --size 256M --name gluster_home vg_data
Format
Create a filesystem on the volume.
Replica
mkfs.ext4 /dev/vg_data/gluster_home
Arbiter
Make sure to add enough inodes on the arbiter. The filesystem for the arbiter is small as it has all the files stored of size 0, but it still needs an inode per file. There is a default filesystem size versus number of inodes ratio, and this ratio can be changed by using -N to set a fixed number of inodes.
mkfs.ext4 -N 131072 /dev/vg_data/gluster_home
Mountpoint
Create the mountpoint.
mkdir /srv/home
fstab
Add the volume to /etc/fstab.
/dev/vg_data/gluster_home /srv/home ext4 defaults 0 0
Mount
Mount the new volume.
mount /srv/home
If the mount command does not succeed, it it most likely because the fstab entry is incorrect.
Software
Mount Point
Glusterfs is not happy about using a directory which is also a mountpoint.
volume create: home: failed: The brick gluster01:/srv/home is a mount point. Please create a sub-directory under the mount point and use that as the brick directory. Or use 'force' at the end of the command if you want to override this behavior.
If for some reason the filesystem is not mounted, then glusterfs might misunderstand the situation and tell the other servers that the directory is now empty, and all files would be deleted on all servers. To avoid this a directory is created under the mount point.
mkdir /srv/home/brick
Install
Install the server.
apt-get install glusterfs-server
If you are running Buster, then make sure the GlusterFS server starts automatically and start it
systemctl enable glusterd.service service glusterd start
Introduce Servers
The GlusterFS servers need to now each other. This can be done from any one server. Here we will do it from gluster01. We need to introduce the two other servers.
gluster peer probe gluster02 gluster peer probe gluster03
Server Status
Now check that the servers were properly probed.
gluster peer status
Number of Peers: 2 Hostname: gluster02 Uuid: c041f1eb-72b5-4737-b25e-4f68c3379ef1 State: Peer in Cluster (Connected) Hostname: gluster03 Uuid: a03ea1dc-5e74-4d1c-aa80-7d0386bce1e7 State: Peer in Cluster (Connected)
Create Volume
Create the gluster volume.
gluster volume create home replica 3 arbiter 1 gluster01:/srv/home/brick gluster02:/srv/home/brick gluster03:/srv/home/brick
Persistent Metadata
Enable consistent metadata for the volume.
gluster volume set home cluster.consistent-metadata on gluster volume set home features.utime on
Start Volume
Finally we can start the volume.
gluster volume start home
Volume Status
Check the status of the volume.
gluster volume status
Status of volume: home Gluster process TCP Port RDMA Port Online Pid ------------------------------------------------------------------------------ Brick gluster01:/srv/home/brick 49152 0 Y 808 Brick gluster02:/srv/home/brick 49152 0 Y 764 Brick gluster03:/srv/home/brick 49152 0 Y 769 Self-heal Daemon on localhost N/A N/A Y 828 Self-heal Daemon on gluster02 N/A N/A Y 785 Self-heal Daemon on gluster03 N/A N/A Y 791 Task Status of Volume home ------------------------------------------------------------------------------ There are no active volume tasks
Volume Information
Check that one of the servers is an arbiter and that it is the correct server.
gluster volume info
Volume Name: home Type: Replicate Volume ID: 26ad72e2-868b-44f1-b51f-24a6eb5f380b Status: Started Snapshot Count: 0 Number of Bricks: 1 x (2 + 1) = 3 Transport-type: tcp Bricks: Brick1: gluster01:/srv/home/brick Brick2: gluster02:/srv/home/brick Brick3: gluster03:/srv/home/brick (arbiter) Options Reconfigured: transport.address-family: inet performance.readdir-ahead: on nfs.disable: on