Distributed Replicated Storage Across Four Storage Nodes With GlusterFS 3.2.x On CentOS 6.3

http://www.howtoforge.com/distributed-replicated-storage-across-four-storage-nodes-with-glusterfs-3.2.x-on-centos-6.3


This tutorial shows how to combine four single storage servers (running CentOS 6.3) to a distributed replicated storage with GlusterFS. Nodes 1 and 2 (replication1) as well as 3 and 4 (replication2) will mirror each other, and replication1 and replication2 will be combined to one larger storage server (distribution). Basically, this is RAID10 over network. If you lose one server from replication1 and one from replication2, the distributed volume continues to work. The client system (CentOS 6.3 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.
I do not issue any guarantee that this will work for you!

1 Preliminary Note

In this tutorial I use five systems, four servers and a client:

• server1.example.com: IP address 192.168.0.100 (server)
• server2.example.com: IP address 192.168.0.101 (server)
• server3.example.com: IP address 192.168.0.102 (server)
• server4.example.com: IP address 192.168.0.103 (server)
• client1.example.com: IP address 192.168.0.104 (client)

All five 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 five systems:

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 server3.example.com server3 192.168.0.103 server4.example.com server4 192.168.0.104 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/server3.example.com/server4.example.com/client1.example.com:
First we import the GPG keys for software packages:
Then we enable the EPEL6 repository on our CentOS systems:
Edit /etc/yum.repos.d/epel.repo...
... and add the line priority=10 to the [epel] section:

[epel] name=Extra Packages for Enterprise Linux 6 - $basearch #baseurl=http://download.fedoraproject.org/pub/epel/6/$basearch mirrorlist=https://mirrors.fedoraproject.org/metalink?repo=epel-6&arch=$basearch failovermethod=priority enabled=1 priority=10 gpgcheck=1 gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL-6 [...]

3 Setting Up The GlusterFS Servers

GlusterFS is available as a package for EPEL, therefore we can install it as follows:
Create the system startup links for the Gluster daemon and start it:
The command
should now show the GlusterFS version that you've just installed (3.2.7 in this case):
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, server2.example.com, server3.example.com, and server4.example.com.
Next we must add server2.example.com, server3.example.com, and server4.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 or server3.example.com or server4.example.com because the configuration is repliacted between the GlusterFS nodes - just make sure you use the correct hostnames or IP addresses):
On server1.example.com, run
Output should be as follows:
The status of the trusted storage pool should now be similar to this:
Next we create the distributed replicated share named testvol with two replicas (please note that the number of replicas is half the number of servers in this case because we want to set up distributed replication) on server1.example.com, server2.example.com, server3.example.com, and server4.example.com in the /data directory (this will be created if it doesn't exist):
Start the volume:
It is possible that the above command tells you that the action was not successful:
In this case you should check the output of...
on both servers.
If you get output like this...
... everything is fine, but if you don't get any output...
... restart the GlusterFS daemon on the corresponding server (server2.example.com, server3.example.com, and server4.example.com in this case):
Then check the output of...
... again on these servers - it should now look like this:
Now back to server1.example.com:
You can check the status of the volume with the command
By default, all clients can connect to the volume. If you want to grant access to client1.example.com (= 192.168.0.104) only, run:
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. 192.168.0.104,192.168.0.105).
The volume info should now show the updated status:

4 Setting Up The GlusterFS Client

On the client, we can install the GlusterFS client as follows:
Then we create the following directory:
That's it! Now we can mount the GlusterFS filesystem to /mnt/glusterfs with the following command:
(Instead of server1.example.com you can as well use server2.example.com or server3.example.com or server4.example.com in the above command!)
You should now see the new share in the outputs of...
... and...
Instead of mounting the GlusterFS share manually on the client, you could modify /etc/fstab so that the share gets mounted automatically when the client boots.
Open /etc/fstab and append the following line:

[...] server1.example.com:/testvol /mnt/glusterfs glusterfs defaults,_netdev 0 0

(Again, instead of server1.example.com you can as well use server2.example.com or server3.example.com or server4.example.com!)
To test if your modified /etc/fstab is working, reboot the client:
After the reboot, you should find the share in the outputs of...
... and...

5 Testing

Now let's create some test files on the GlusterFS share:
Now let's check the /data directory on server1.example.com, server2.example.com, server3.example.com, and server4.example.com. You will notice that replication1 as well as replication2 hold only a part of the files/directories that make up the GlusterFS share on the client, but the nodes that make up replication1 (server1 and server2) or replication2 (server3 and server4) contain the same files (mirroring):
Now we shut down server1.example.com and server4.example.com and add/delete some files on the GlusterFS share on client1.example.com.
The changes should be visible in the /data directory on server2.example.com and server3.example.com:
Let's boot server1.example.com and server4.example.com again and take a look at the /data directory:
As you see, server1.example.com and server4.example.com haven't noticed the changes that happened while they were down. 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.:
Now take a look at the /data directory on server1.example.com and server4.example.com again, and you should see that the changes have been replicated to these nodes:

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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