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

Version 1.0
Author: Falko Timme <ft [at] falkotimme [dot] com>
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Last edited 12/17/2012

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:

vi /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   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:

rpm --import /etc/pki/rpm-gpg/RPM-GPG-KEY*

Then we enable the EPEL6 repository on our CentOS systems:

rpm --import https://fedoraproject.org/static/0608B895.txt

cd /tmp
wget http://dl.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-7.noarch.rpm
rpm -ivh epel-release-6-7.noarch.rpm

yum install yum-priorities

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

vi /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

server1.example.com/server2.example.com/server3.example.com/server4.example.com:

GlusterFS is available as a package for EPEL, therefore we can install it as follows:

yum install glusterfs-server

Create the system startup links for the Gluster daemon and start it:

chkconfig --levels 235 glusterd on
/etc/init.d/glusterd start

The command

glusterfsd --version

should now show the GlusterFS version that you've just installed (3.2.7 in this case):

[root@server1 ~]# glusterfsd --version
glusterfs 3.2.7 built on Jun 11 2012 13:22:28
Repository revision: git://git.gluster.com/glusterfs.git
Copyright (c) 2006-2011 Gluster Inc. <http://www.gluster.com>
GlusterFS comes with ABSOLUTELY NO WARRANTY.
You may redistribute copies of GlusterFS under the terms of the GNU General Public License.
[root@server1 ~]#

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):

server1.example.com:

On server1.example.com, run

gluster peer probe server2.example.com
gluster peer probe server3.example.com
gluster peer probe server4.example.com

Output should be as follows:

[root@server1 ~]# gluster peer probe server2.example.com
Probe successful
[root@server1 ~]#

The status of the trusted storage pool should now be similar to this:

gluster peer status

[root@server1 ~]# gluster peer status
Number of Peers: 3

Hostname: server2.example.com
Uuid: 600ff607-f7fd-43f6-af8d-419df703376d
State: Peer in Cluster (Connected)

Hostname: server3.example.com
Uuid: 1d6a5f3f-c2dd-4727-a050-0431772cc381
State: Peer in Cluster (Connected)

Hostname: server4.example.com
Uuid: 0bd9d445-0b5b-4a91-be6f-02b13c41d5d6
State: Peer in Cluster (Connected)
[root@server1 ~]#

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):

gluster volume create testvol replica 2 transport tcp server1.example.com:/data server2.example.com:/data server3.example.com:/data server4.example.com:/data

[root@server1 ~]# gluster volume create testvol replica 2 transport tcp server1.example.com:/data server2.example.com:/data server3.example.com:/data server4.example.com:/data
Creation of volume testvol has been successful. Please start the volume to access data.
[root@server1 ~]#

Start the volume:

gluster volume start testvol

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/server3.example.com/server4.example.com:

netstat -tap | grep glusterfsd

on both servers.

If you get output like this...

[root@server1 ~]# netstat -tap | grep glusterfsd
tcp        0      0 *:24009                     *:*                         LISTEN      1365/glusterfsd
tcp        0      0 localhost:1023              localhost:24007             ESTABLISHED 1365/glusterfsd
tcp        0      0 server1.example.com:24009   server1.example.com:1023    ESTABLISHED 1365/glusterfsd
[root@server1 ~]#

... everything is fine, but if you don't get any output...

[root@server2 ~]# netstat -tap | grep glusterfsd
[root@server2 ~]#

[root@server3 ~]# netstat -tap | grep glusterfsd
[root@server3 ~]#

[root@server4 ~]# netstat -tap | grep glusterfsd
[root@server4 ~]#

... restart the GlusterFS daemon on the corresponding server (server2.example.com, server3.example.com, and server4.example.com in this case):

server2.example.com/server3.example.com/server4.example.com:

/etc/init.d/glusterfsd restart

Then check the output of...

netstat -tap | grep glusterfsd

... again on these servers - it should now look like this:

[root@server2 ~]# netstat -tap | grep glusterfsd
tcp        0      0 *:24009                 *:*                     LISTEN      1152/glusterfsd
tcp        0      0 localhost.localdom:1018 localhost.localdo:24007 ESTABLISHED 1152/glusterfsd
[root@server2 ~]#

[root@server3 ~]# netstat -tap | grep glusterfsd
tcp        0      0 *:24009                 *:*                     LISTEN      1311/glusterfsd
tcp        0      0 localhost.localdom:1018 localhost.localdo:24007 ESTABLISHED 1311/glusterfsd
[root@server3 ~]#

[root@server4 ~]# netstat -tap | grep glusterfsd
tcp        0      0 *:24009                 *:*                     LISTEN      1297/glusterfsd
tcp        0      0 localhost.localdom:1019 localhost.localdo:24007 ESTABLISHED 1297/glusterfsd
[root@server4 ~]#

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: Distributed-Replicate
Status: Started
Number of Bricks: 2 x 2 = 4
Transport-type: tcp
Bricks:
Brick1: server1.example.com:/data
Brick2: server2.example.com:/data
Brick3: server3.example.com:/data
Brick4: server4.example.com:/data
[root@server1 ~]#

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:

gluster volume set testvol auth.allow 192.168.0.104

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:

gluster volume info

[root@server1 ~]# gluster volume info

Volume Name: testvol
Type: Distributed-Replicate
Status: Started
Number of Bricks: 2 x 2 = 4
Transport-type: tcp
Bricks:
Brick1: server1.example.com:/data
Brick2: server2.example.com:/data
Brick3: server3.example.com:/data
Brick4: server4.example.com:/data
Options Reconfigured:
auth.allow: 192.168.0.104
[root@server1 ~]#