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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 one as the arbiter. |
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| * 192.168.1.44 gluster05 * 192.168.1.45 gluster06 * 192.168.1.46 gluster07 |
* 192.168.1.44 gluster05 (replica) * 192.168.1.45 gluster06 (replica) * 192.168.1.46 gluster07 (arbiter) |
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| To keep things separated the OS will be on one disk and the glusterfs filesystem will be on another disk. We will [[Domain Editing|add a disk]] to the domain. This disk will be used for the glusterfs file storage. | 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 [[Domain Editing|add a disk]] to the domain. This disk will be used for the GlusterFS file storage. |
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| Set up a new physical volume, configure a volume group and add a volume | Set up a new physical volume, configure a volume group. |
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| lvcreate --size 4G --name gluster_www vg2 | }}} ===== Replica ===== Add a volume {{{ lvcreate --size 4G --name gluster_home vg2 }}} ===== Arbiter ===== Add a volume {{{ lvcreate --size 512M --name gluster_home vg2 |
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| mkfs.btrfs /dev/vg2/gluster_www | mkfs.btrfs /dev/vg2/gluster_home |
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| mkdir /srv/www | mkdir /srv/home |
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| /dev/vg2/gluster_www /srv/www btrfs defaults 0 0 | /dev/vg2/gluster_www /srv/home btrfs defaults 0 0 |
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| mount /srv/www | mount /srv/home |
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| ''volume create: www: failed: The brick gluster01:/srv/www 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.'' | ''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.'' |
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| mkdir /srv/www/brick | mkdir /srv/home/brick |
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| 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 three other servers. | The GlusterFS servers need to now each other. This can be done from any one server. Here we will do it from gluster05. We need to introduce the two other servers. |
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| gluster peer probe gluster02 gluster peer probe gluster03 gluster peer probe gluster04 |
gluster peer probe gluster06 gluster peer probe gluster07 |
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| Number of Peers: 3 | Number of Peers: 2 |
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| Hostname: gluster02 Uuid: 031573c2-3b1f-4946-bd78-421563249db6 |
Hostname: gluster06 Uuid: c041f1eb-72b5-4737-b25e-4f68c3379ef1 |
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| Hostname: gluster03 Uuid: ff5cec1c-6d7f-4db7-8676-08deff06b4d0 State: Peer in Cluster (Connected) Hostname: gluster04 Uuid: 65fc398a-52e9-4292-9bbb-884becfbf5d6 |
Hostname: gluster07 Uuid: a03ea1dc-5e74-4d1c-aa80-7d0386bce1e7 |
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| gluster volume create www replica 4 transport tcp gluster01:/srv/www/brick gluster02:/srv/www/brick gluster03:/srv/www/brick gluster04:/srv/www/brick | gluster volume create home replica 3 arbiter 1 gluster05:/srv/home/brick gluster06:/srv/home/brick gluster07:/srv/home/brick |
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| gluster volume start www | gluster volume start home |
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| Status of volume: www | Status of volume: home |
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| Brick gluster01:/srv/www 49152 0 Y 826 Brick gluster02:/srv/www 49152 0 Y 1355 Brick gluster03:/srv/www 49152 0 Y 1034 Brick gluster04:/srv/www 49152 0 Y 1135 Self-heal Daemon on localhost N/A N/A Y 846 Self-heal Daemon on gluster02 N/A N/A Y 1377 Self-heal Daemon on gluster03 N/A N/A Y 1054 Self-heal Daemon on gluster04 N/A N/A Y 1155 |
Brick gluster05:/srv/home/brick 49152 0 Y 808 Brick gluster06:/srv/home/brick 49152 0 Y 764 Brick gluster07:/srv/home/brick 49152 0 Y 769 Self-heal Daemon on localhost N/A N/A Y 828 Self-heal Daemon on gluster06 N/A N/A Y 785 Self-heal Daemon on gluster07 N/A N/A Y 791 |
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| Task Status of Volume www | Task Status of Volume home |
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=== Volume Information === Lets check that one of the volumes is an arbiter {{{ 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: gluster05:/srv/home/brick Brick2: gluster06:/srv/home/brick Brick3: gluster07:/srv/home/brick (arbiter) Options Reconfigured: transport.address-family: inet performance.readdir-ahead: on nfs.disable: on }}} |
GlusterFS Server and 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 one 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.
- 192.168.1.44 gluster05 (replica)
- 192.168.1.45 gluster06 (replica)
- 192.168.1.46 gluster07 (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 vg2 /dev/vdb1
Replica
Add a volume
lvcreate --size 4G --name gluster_home vg2
Arbiter
Add a volume
lvcreate --size 512M --name gluster_home vg2
Format
Create a filesystem on the volume.
mkfs.btrfs /dev/vg2/gluster_home
Mountpoint
Create the mountpoint.
mkdir /srv/home
fstab
Add the volume to /etc/fstab.
/dev/vg2/gluster_www /srv/home btrfs 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
Introduce Servers
The GlusterFS servers need to now each other. This can be done from any one server. Here we will do it from gluster05. We need to introduce the two other servers.
gluster peer probe gluster06 gluster peer probe gluster07
Server Status
Now check that the servers were properly probed.
gluster peer status
Number of Peers: 2 Hostname: gluster06 Uuid: c041f1eb-72b5-4737-b25e-4f68c3379ef1 State: Peer in Cluster (Connected) Hostname: gluster07 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 gluster05:/srv/home/brick gluster06:/srv/home/brick gluster07:/srv/home/brick
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 gluster05:/srv/home/brick 49152 0 Y 808 Brick gluster06:/srv/home/brick 49152 0 Y 764 Brick gluster07:/srv/home/brick 49152 0 Y 769 Self-heal Daemon on localhost N/A N/A Y 828 Self-heal Daemon on gluster06 N/A N/A Y 785 Self-heal Daemon on gluster07 N/A N/A Y 791 Task Status of Volume home ------------------------------------------------------------------------------ There are no active volume tasks
Volume Information
Lets check that one of the volumes is an arbiter
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: gluster05:/srv/home/brick Brick2: gluster06:/srv/home/brick Brick3: gluster07:/srv/home/brick (arbiter) Options Reconfigured: transport.address-family: inet performance.readdir-ahead: on nfs.disable: on