High-Availability Storage With GlusterFS 3.2.x On Ubuntu 11.10 - Automatic File Replication Across Two Storage Servers

This tutorial shows how to set up a high-availability storage with two storage servers (Ubuntu 11.10) 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 (Ubuntu 11.10 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 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)

Because we will run all the steps from this tutorial with root privileges, we can either prepend all commands in this tutorial with the string sudo, or we become root right now by typing
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:

127.0.0.1 localhost.localdomain localhost 192.168.0.100 server1.example.com server1 192.168.0.101 server2.example.com server2 192.168.0.102 client1.example.com client1 # The following lines are desirable for IPv6 capable hosts ::1 localhost ip6-localhost ip6-loopback fe00::0 ip6-localnet ff00::0 ip6-mcastprefix ff02::1 ip6-allnodes ff02::2 ip6-allrouters ff02::3 ip6-allhosts

(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 Setting Up The GlusterFS Servers

GlusterFS is available as a package for Ubuntu 11.10, therefore we can install it as follows:
The command
should now show the GlusterFS version that you've just installed (3.2.1 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 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):
On server1.example.com, run
The status of the trusted storage pool should now be similar to this:
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):
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 in this case):
Then check the output of...
... again on that server - 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 (= 192.168.0.102) 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. 192.168.0.102,192.168.0.103).
The volume info should now show the updated status:

3 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 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!)
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...

4 Testing

Now let's create some test files on the GlusterFS share:
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:
Now we shut down server1.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:
Let's boot server1.example.com again and take a look at the /data directory:
As you see, server1.example.com hasn't noticed the changes that happened while it was 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 again, and you should see that the changes have been replicated to that node:

5 Links

• GlusterFS: http://www.gluster.org/
• GlusterFS 3.2 Documentation: http://download.gluster.com/pub/gluster/glusterfs/3.2/Documentation/AG/html/index.html
• Ubuntu: http://www.ubuntu.com/

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