How To Configure Data Replication/Synchronize on CentOS 6 Using DRBD

This article will explain how to configure data replication/synchronize using DRBD application. According this article : http://drbd.linbit.com/
DRBD® refers to block devices designed as a building block to form high availability (HA) clusters. This is done by mirroring a whole block device via an assigned network. DRBD can be understood as network based raid-1.
For configure DRBD, we should have at least 2 machines and have 2 harddrive on each machines. One harddrive will be configured as OS system and one harddrive will be configured as harddrive for replication with other harddrive on other machine
drbd-topology
In this guidance, i am build 2 systems for replication. The systems using CentOS 6 64 Bit. For easy understanding, this is my information system
# Server 1
Hostname   : node1
Domain     : imanudin.net
IP Address : 192.168.80.91

# Server 2
Hostname   : node2
Domain     : imanudin.net
IP Address : 192.168.80.92

# Second Harddrive 1 GB on each machines for testing Purpose
# Configure Network
First, we must configure network on CentOS. Assuming name of your network interface is eth0. Do the following configuration on all nodes (node1 and node2) and adjust on node2

1.vi /etc/sysconfig/network-scripts/ifcfg-eth0
DEVICE=eth0
ONBOOT=yes
NM_CONTROLLED=no
BOOTPROTO=none
IPADDR=192.168.80.91
NETMASK=255.255.255.0
DNS1=192.168.80.91
GATEWAY=192.168.80.11
DNS2=192.168.80.11
DNS3=8.8.8.8
USERCTL=no
Restart network service and setup for automatic boot on all nodes (node1 and node2)

1.service network restart
2.chkconfig network on
# Configure Disable Selinux & Firewall on all nodes (node1 and node2)
Open file /etc/sysconfig/selinux and change SELINUX=enforcing become SELINUX=disabled. Also disable some service such as iptables and ip6tables.

1.setenforce 0
2.service iptables stop
3.service ip6tables stop
4.chkconfig iptables off
5.chkconfig ip6tables off
# Configure /etc/hosts and hostname on all nodes (node1 and node2)
Open file /etc/hosts and configure as follows on all nodes (node1 and node2)
127.0.0.1     localhost
192.168.80.91 node1.imanudin.net node1
192.168.80.92 node2.imanudin.net node2
Do the following command as root and open file /etc/sysconfig/network to change hostname
– On node1

1.hostname node1.imanudin.net
2.vi /etc/sysconfig/network
Change HOSTNAME so that like below :
NETWORKING=yes
HOSTNAME=node1.imanudin.net
– On node2

1.hostname node2.imanudin.net
2.vi /etc/sysconfig/network
Change HOSTNAME so that like below :
NETWORKING=yes
HOSTNAME=node2.imanudin.net
# Update repos and install packages DRBD on all nodes (node1 and node2)

1.wget http://www.elrepo.org/elrepo-release-6-6.el6.elrepo.noarch.rpm
2.rpm -ivh elrepo-release-6-6.el6.elrepo.noarch.rpm
3.yum update
4.yum install kmod-drbd83 drbd83-utils
# Configure DRBD
– Configure file /etc/drbd.conf (enough on node1 only)

1.vi /etc/drbd.conf
fill with the following line
global {
dialog-refresh 1;
usage-count yes;
minor-count 5;
}
common {
syncer {
rate 10M;
}
}
resource r0 {
startup {
wfc-timeout 30;
outdated-wfc-timeout 20;
degr-wfc-timeout 120;
}
protocol C;
disk {
on-io-error detach;
}
syncer {
rate 10M;
al-extents 257;
}
on node1.imanudin.net {
device /dev/drbd0;
address 192.168.80.91:7788;
meta-disk internal;
disk /dev/sdb;
}
on node2.imanudin.net {
device /dev/drbd0;
address 192.168.80.92:7788;
meta-disk internal;
disk /dev/sdb;
}
}

Note :
r0 is resources name for DRBD.
/dev/sdb is second drive on each machines that will configured for DRBD. Please check with fdisk -l command to make sure the name of second drive. Recommended capacity harddrive on each machines are same. If different, the bigger harddrive will adjust with the lower harddrive.
Recommended using 2 NIC for each machines. 1 NIC for communication with clients and 1 NIC for communication between servers using Cross cable (DRBD communication)
# Copy drbd.conf from node1 to node2 (run the following command on node1)

1.scp /etc/drbd.conf root@node2:/etc/drbd.conf
# Create metadata on all nodes (node1 and node2)
Run the following command

1.drbdadm create-md r0
# Start DRBD services on all nodes (node1 and node2)
Run the following command

1.service drbd start
2.chkconfig drbd on
# Check DRBD status all nodes (node1 and node2)

1.service drbd status
# Configure primary DRBD on node1
Run the following command only at node1

1.drbdsetup /dev/drbd0 primary --overwrite-data-of-peer
Please wait until 100% synchronize devices among node1 and node2. You also could check the progress with the following command

1.service drbd status
2.watch service drbd status
After finish synchronization, you will see Connected and UpToDate among node1 and node2
drbd driver loaded OK; device status:
version: 8.4.5 (api:1/proto:86-101)
GIT-hash: 1d360bde0e095d495786eaeb2a1ac76888e4db96 build by phil@Build64R6, 2014-10-28 10:32:53
m:res cs ro ds p mounted fstype
0:r0 Connected Primary/Secondary UpToDate/UpToDate C
# Format device DRBD
In this section, i am using ext3. You can using other format such as xfs, ext4 and other

1.mkfs.ext3 /dev/drbd0
Hooray, finally DRBD has been finished configured and connected each other

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