This tutorial shows how to set up a high-availability storage with two storage servers (CentOS 7.2) that use GlusterFS. Each storage server will be a mirror of the other storage server, and files will be replicated automatically across both storage servers. The client system (CentOS 7.2 as well) will be able to access the storage as if it was a local filesystem. GlusterFS is a clustered file-system capable of scaling to several peta-bytes. It aggregates various storage bricks over Infiniband RDMA or TCP/IP interconnect into one large parallel network file system. Storage bricks can be made of any commodity hardware such as x86_64 servers with SATA-II RAID and Infiniband HBA.

1 Preliminary Note
In this tutorial I use three systems, two servers, and a client:
server1.example.com: IP address 192.168.0.100 (server)
server2.example.com: IP address 192.168.0.101 (server)
client1.example.com: IP address 192.168.0.102 (client)
All three systems should be able to resolve the other systems’ hostnames. If this cannot be done through DNS, you should edit the /etc/hosts file so that it looks as follows on all three systems:
nano /etc/hosts

127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4
192.168.0.100 server1.example.com server1
192.168.0.101 server2.example.com server2
192.168.0.102 client1.example.com client1

::1 localhost localhost.localdomain localhost6 localhost6.localdomain6
(It is also possible to use IP addresses instead of hostnames in the following setup. If you prefer to use IP addresses, you don’t have to care about whether the hostnames can be resolved or not.)

2 Enable additional Repositories
server1.example.com/server2.example.com/client1.example.com:
First, we import the GPG keys for software packages:
rpm –import /etc/pki/rpm-gpg/RPM-GPG-KEY*

Then we enable the EPEL 7 repository on our CentOS systems:
yum -y install epel-release

yum -y install yum-priorities

Edit /etc/yum.repos.d/epel.repo…
nano /etc/yum.repos.d/epel.repo

… and add the line priority=10 to the [epel] section:
[epel]
name=Extra Packages for Enterprise Linux 7 – $basearch
#baseurl=http://download.fedoraproject.org/pub/epel/7/$basearch
mirrorlist=https://mirrors.fedoraproject.org/metalink?repo=epel-7&arch=$basearch
failovermethod=priority
enabled=1
priority=10
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL-7
[…]
Then we update our existing packages on the system:
yum -y update
3 Setting up the GlusterFS Servers
server1.example.com/server2.example.com:
GlusterFS is available in the repository of the CentOS storage special interest group. Install the repository with this command:
yum -y install centos-release-gluster

Then install the GlusterFS server as follows:
yum -y install glusterfs-server

Create the system startup links for the Gluster daemon and start it:
systemctl enable glusterd.service
systemctl start glusterd.service

The command
glusterfsd –version

should now show the GlusterFS version that you’ve just installed (3.7.12 in this case):
[root@server1 ~]# glusterfsd –version
glusterfs 3.7.12 built on Jun 24 2016 14:11:19
Repository revision: git://git.gluster.com/glusterfs.git
Copyright (c) 2006-2013 Red Hat, Inc. <http://www.redhat.com/>
GlusterFS comes with ABSOLUTELY NO WARRANTY.
It is licensed to you under your choice of the GNU Lesser
General Public License, version 3 or any later version (LGPLv3
or later), or the GNU General Public License, version 2 (GPLv2),
in all cases as published by the Free Software Foundation.
If you use a firewall, ensure that TCP ports 111, 24007, 24008, 24009-(24009 + number of bricks across all volumes) are open on server1.example.com and server2.example.com.
Next, we must add server2.example.com to the trusted storage pool (please note that I’m running all GlusterFS configuration commands from server1.example.com, but you can as well run them from server2.example.com because the configuration is repliacted between the GlusterFS nodes – just make sure you use the correct hostnames or IP addresses):
server1.example.com:
On server1.example.com, run
gluster peer probe server2.example.com

[root@server1 ~]# gluster peer probe server2.example.com
peer probe: success.
The status of the trusted storage pool should now be similar to this:
gluster peer status

[root@server1 ~]# gluster peer status
Number of Peers: 1
Hostname: server2.example.com
Uuid: 582e10da-aa1b-40b8-908c-213f16f57fe5
State: Peer in Cluster (Connected)
Next, we create the share named testvol with two replicas (please note that the number of replicas is equal to the number of servers in this case because we want to set up mirroring) on server1.example.com and server2.example.com in the /data directory (this will be created if it doesn’t exist):
gluster volume create testvol replica 2 transport tcp server1.example.com:/data server2.example.com:/data force

[root@server1 ~]# gluster volume create testvol replica 2 transport tcp server1.example.com:/data server2.example.com:/data force
volume create: testvol: success: please start the volume to access data
[root@server1 ~]#
Start the volume:
gluster volume start testvol

The result should be:
[root@server1 ~]# gluster volume start testvol
volume start: testvol: success
[root@server1 ~]#
It is possible that the above command tells you that the action was not successful:
[root@server1 ~]# gluster volume start testvol
Starting volume testvol has been unsuccessful
[root@server1 ~]#
In this case, you should check the output of…
server1.example.com/server2.example.com:
netstat -tap | grep glusterfsd

on both servers.
If you get output like this…
[root@server1 ~]# netstat -tap | grep glusterfsd
tcp 0 0 0.0.0.0:49152 0.0.0.0:* LISTEN 22880/glusterfsd
tcp 0 0 server1.example.c:49152 server2.example.c:49148 ESTABLISHED 22880/glusterfsd
tcp 0 0 server1.example.c:49152 server1.example.c:49148 ESTABLISHED 22880/glusterfsd
tcp 0 0 server1.example.c:49150 server1.example.c:24007 ESTABLISHED 22880/glusterfsd
tcp 0 0 server1.example.c:49152 server2.example.c:49142 ESTABLISHED 22880/glusterfsd
tcp 0 0 server1.example.c:49152 server1.example.c:49149 ESTABLISHED 22880/glusterfsd
[root@server1 ~]#
… everything is fine, but if you don’t get any output…
[root@server2 ~]# netstat -tap | grep glusterfsd
[root@server2 ~]#
… restart the GlusterFS daemon on the corresponding server (server2.example.com in this case):
server2.example.com:
systemctl restart glusterd.service

Then check the output of…
netstat -tap | grep glusterfsd

… again on that server – it should now look like this:
[root@server2 ~]# netstat -tap | grep glusterfsd
tcp 0 0 0.0.0.0:49152 0.0.0.0:* LISTEN 10971/glusterfsd
tcp 0 0 server2.example.c:49152 server1.example.c:49140 ESTABLISHED 10971/glusterfsd
tcp 0 0 server2.example.c:49152 server2.example.c:49149 ESTABLISHED 10971/glusterfsd
tcp 0 0 server2.example.c:49152 server2.example.c:49143 ESTABLISHED 10971/glusterfsd
tcp 0 0 server2.example.c:49152 server1.example.c:49142 ESTABLISHED 10971/glusterfsd
tcp 0 0 server2.example.c:49150 server2.example.c:24007 ESTABLISHED 10971/glusterfsd
[root@server2 ~]#
Now back to server1.example.com:
server1.example.com:
You can check the status of the volume with the command
gluster volume info

[root@server1 ~]# gluster volume info
Volume Name: testvol
Type: Replicate
Volume ID: e1f825ca-c9d9-4eeb-b6c5-d62c4aa02376
Status: Started
Number of Bricks: 1 x 2 = 2
Transport-type: tcp
Bricks:
Brick1: server1.example.com:/data
Brick2: server2.example.com:/data
Options Reconfigured:
performance.readdir-ahead: on
[root@server1 ~]#
By default, all clients can connect to the volume. If you want to grant access to client1.example.com (= 192.168.1.102) only, run:
gluster volume set testvol auth.allow 192.168.1.102

Please note that it is possible to use wildcards for the IP addresses (like 192.168.*) and that you can specify multiple IP addresses separated by comma (e.g. 192.168.1.102,192.168.1.103).
The volume info should now show the updated status:
gluster volume info

[root@server1 ~]# gluster volume info
Volume Name: testvol
Type: Replicate
Volume ID: e1f825ca-c9d9-4eeb-b6c5-d62c4aa02376
Status: Started
Number of Bricks: 1 x 2 = 2
Transport-type: tcp
Bricks:
Brick1: server1.example.com:/data
Brick2: server2.example.com:/data
Options Reconfigured:
auth.allow: 192.168.1.102
performance.readdir-ahead: on
[root@server1 ~]#

4 Setting Up the GlusterFS Client
client1.example.com:
On the client, we can install the GlusterFS client as follows:
yum -y install glusterfs-client

Then we create the following directory:
mkdir /mnt/glusterfs

That’s it! Now we can mount the GlusterFS filesystem to /mnt/glusterfs with the following command:
mount.glusterfs server1.example.com:/testvol /mnt/glusterfs

(Instead of server1.example.com you can as well use server2.example.com in the above command!)
You should now see the new share in the outputs of…
mount

[root@client1 ~]# mount
sysfs on /sys type sysfs (rw,nosuid,nodev,noexec,relatime,seclabel)
proc on /proc type proc (rw,nosuid,nodev,noexec,relatime)
devtmpfs on /dev type devtmpfs (rw,nosuid,seclabel,size=930336k,nr_inodes=232584,mode=755)
securityfs on /sys/kernel/security type securityfs (rw,nosuid,nodev,noexec,relatime)
tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev,seclabel)
devpts on /dev/pts type devpts (rw,nosuid,noexec,relatime,seclabel,gid=5,mode=620,ptmxmode=000)
tmpfs on /run type tmpfs (rw,nosuid,nodev,seclabel,mode=755)
tmpfs on /sys/fs/cgroup type tmpfs (ro,nosuid,nodev,noexec,seclabel,mode=755)
cgroup on /sys/fs/cgroup/systemd type cgroup (rw,nosuid,nodev,noexec,relatime,xattr,release_agent=/usr/lib/systemd/systemd-cgroups-agent,name=systemd)
pstore on /sys/fs/pstore type pstore (rw,nosuid,nodev,noexec,relatime)
cgroup on /sys/fs/cgroup/cpuset type cgroup (rw,nosuid,nodev,noexec,relatime,cpuset)
cgroup on /sys/fs/cgroup/hugetlb type cgroup (rw,nosuid,nodev,noexec,relatime,hugetlb)
cgroup on /sys/fs/cgroup/devices type cgroup (rw,nosuid,nodev,noexec,relatime,devices)
cgroup on /sys/fs/cgroup/cpu,cpuacct type cgroup (rw,nosuid,nodev,noexec,relatime,cpuacct,cpu)
cgroup on /sys/fs/cgroup/blkio type cgroup (rw,nosuid,nodev,noexec,relatime,blkio)
cgroup on /sys/fs/cgroup/memory type cgroup (rw,nosuid,nodev,noexec,relatime,memory)
cgroup on /sys/fs/cgroup/perf_event type cgroup (rw,nosuid,nodev,noexec,relatime,perf_event)
cgroup on /sys/fs/cgroup/freezer type cgroup (rw,nosuid,nodev,noexec,relatime,freezer)
cgroup on /sys/fs/cgroup/net_cls type cgroup (rw,nosuid,nodev,noexec,relatime,net_cls)
configfs on /sys/kernel/config type configfs (rw,relatime)
/dev/mapper/centos-root on / type xfs (rw,relatime,seclabel,attr2,inode64,noquota)
selinuxfs on /sys/fs/selinux type selinuxfs (rw,relatime)
systemd-1 on /proc/sys/fs/binfmt_misc type autofs (rw,relatime,fd=34,pgrp=1,timeout=300,minproto=5,maxproto=5,direct)
debugfs on /sys/kernel/debug type debugfs (rw,relatime)
mqueue on /dev/mqueue type mqueue (rw,relatime,seclabel)
hugetlbfs on /dev/hugepages type hugetlbfs (rw,relatime,seclabel)
/dev/sda1 on /boot type xfs (rw,relatime,seclabel,attr2,inode64,noquota)
tmpfs on /run/user/0 type tmpfs (rw,nosuid,nodev,relatime,seclabel,size=188060k,mode=700)
server1.example.com:/testvol on /mnt/glusterfs type fuse.glusterfs (rw,relatime,user_id=0,group_id=0,default_permissions,allow_other,max_read=131072)
fusectl on /sys/fs/fuse/connections type fusectl (rw,relatime)
[root@client1 ~]#

… and…
df -h

[root@client1 ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/centos-root 28G 1.3G 27G 5% /
devtmpfs 909M 0 909M 0% /dev
tmpfs 919M 0 919M 0% /dev/shm
tmpfs 919M 8.6M 910M 1% /run
tmpfs 919M 0 919M 0% /sys/fs/cgroup
/dev/sda1 497M 192M 306M 39% /boot
tmpfs 184M 0 184M 0% /run/user/0
server1.example.com:/testvol 28G 12G 17G 41% /mnt/glusterfs
[root@client1 ~]#
Instead of mounting the GlusterFS share manually on the client, you add the mount command to /etc/rc.local file. I will not add it to /etc/fstab as rc.local is always executed after the network is up which is required for a network file system
Open /etc/rc.local and append the following line:
nano /etc/rc.local

[…]
/usr/sbin/mount.glusterfs server1.example.com:/testvol /mnt/glusterfs
(Again, instead of server1.example.com you can as well use server2.example.com!)
To test if your modified /etc/rc.local is working, reboot the client:
reboot

After the reboot, you should find the share in the outputs of…
df -h

… and…
mount
5 Testing
Now let’s create some test files on the GlusterFS share:
client1.example.com:
touch /mnt/glusterfs/test1
touch /mnt/glusterfs/test2

Now let’s check the /data directory on server1.example.com and server2.example.com. The test1 and test2 files should be present on each node:
server1.example.com/server2.example.com:
ls -l /data

[root@server1 ~]# ls -l /data
total 0
-rw-r–r–. 2 root root 0 Jul 1 2016 test1
-rw-r–r–. 2 root root 0 Jul 1 2016 test2
[root@server1 ~]
Now we shut down server1.example.com and add/delete some files on the GlusterFS share on client1.example.com.
server1.example.com:
shutdown -h now

client1.example.com:
touch /mnt/glusterfs/test3
touch /mnt/glusterfs/test4
rm -f /mnt/glusterfs/test2

The commands may take some time to execute as the Glusterfs switches to server2 after he can not reach server1 anymore. We can see here the fault tolerance of the system as we can still work on our data storage share when server1 is offline. The changes should be visible in the /data directory on server2.example.com:
server2.example.com:
ls -l /data

[root@server2 ~]# ls -l /data
total 8
-rw-r–r–. 2 root root 0 Jul 1 15:17 test1
-rw-r–r–. 2 root root 0 Jul 1 15:19 test3
-rw-r–r–. 2 root root 0 Jul 1 15:19 test4
Let’s boot server1.example.com again and take a look at the /data directory:
server1.example.com:
ls -l /data

[root@server1 ~]# ls -l /data
total 8
-rw-r–r–. 2 root root 0 Jul 1 15:17 test1
-rw-r–r–. 2 root root 0 Jul 1 15:19 test2
[root@server1 ~]#
As you see, server1.example.com automatically synced the changed. In case that the change has not been synced yet, then this is easy to fix, all we need to do is invoke a read command on the GlusterFS share on client1.example.com, e.g.:
client1.example.com:
ls -l /mnt/glusterfs/

[root@client1 ~]# ls -l /data
total 8
-rw-r–r–. 2 root root 0 Jul 1 15:17 test1
-rw-r–r–. 2 root root 0 Jul 1 15:19 test3
-rw-r–r–. 2 root root 0 Jul 1 15:19 test4
[root@server1 ~]#
Now take a look at the /data directory on server1.example.com again, and you should see that the changes have been replicated to that node:
server1.example.com:
ls -l /data

[root@server1 ~]# ls -l /data
total 8
-rw-r–r–. 2 root root 0 Jul 1 15:17 test1
-rw-r–r–. 2 root root 0 Jul 1 15:19 test3
-rw-r–r–. 2 root root 0 Jul 1 15:19 test4
[root@server1 ~]#

6 Links
GlusterFS: http://www.gluster.org/
GlusterFS 3.2 Documentation: http://download.gluster.com/pub/gluster/glusterfs/3.2/Documentation/AG/html/index.html
CentOS: http://www.centos.org/

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