How To Install DRBD On CentOS Linux?

DRBD (Distributed Replicated Block Device) is a powerful software tool designed for Linux systems. It enables the replication of storage devices over a network, providing solutions for disaster recovery and failover management. Essentially, DRBD creates a network-based alternative to shared storage, ensuring high availability and reliability for your hardware resources.

What You'll Learn

How DRBD Works

DRBD allows the creation of a virtual block device (/dev/drbd0) that mirrors physical block devices (e.g., /dev/sdb1) between two systems. These systems are designated as the primary and secondary nodes, with the primary node handling read/write operations.

Here’s how it operates:

1. Storage Clustering: DRBD replicates the data on a block device from the primary node to the secondary node.

2. Failover Mechanism: If the primary node fails, the secondary node can seamlessly take over by becoming the new primary.

3. Data Integrity: The synchronization process ensures that the data remains consistent across nodes.

Using DRBD on CentOS

This guide focuses on configuring DRBD on CentOS 7 but is applicable to other CentOS versions.

Requirements

• Two CentOS systems.

• A free block device on each system, e.g., /dev/sdb1.

• SELinux set to permissive or disabled.

• Port 7788 open on the firewall.

• Both nodes must be on the same network.

Installation Steps

1. Add the EPEL Repository

   Install the ELRepo package since DRBD is not included in the default CentOS repositories:

   bash Copy

   
   rpm -ivh http://www.elrepo.org/elrepo-release-7.0-2.el7.elrepo.noarch.rpm
   rpm --import /etc/pki/rpm-gpg/RPM-GPG-KEY-elrepo.org
                                       

2. Install DRBD

   Use yum to install the DRBD package and kernel modules:

   bash Copy

   
   yum -y install drbd84-utils kmod-drbd84
                                       

3. Verify Kernel Module

   Check if the DRBD kernel module is loaded:

   bash Copy

   
   lsmod | grep -i drbd
                                       

   If not loaded, reboot the system and load it manually:

   bash Copy

   
   modprobe drbd
   echo drbd > /etc/modules-load.d/drbd.conf
                                       

Configuring DRBD

1. Create a Resource File

   Resource files define the DRBD configuration. On both nodes, create a resource file, e.g., linuxhandbook.res:

   bash Copy

   
   vi /etc/drbd.d/linuxhandbook.res
                                       

   Add the following configuration:

   plaintext Copy

   
   resource linuxhandbook {
       protocol C;
       on node1 {
           device /dev/drbd0;
           disk /dev/sdb1;
           address 10.20.222.14:7788;
           meta-disk internal;
       }
       on node2 {
           device /dev/drbd0;
           disk /dev/sdb1;
           address 10.20.222.15:7788;
           meta-disk internal;
       }
   }
                                       

2. Initialize Metadata

   Prepare the block devices for DRBD:

   bash Copy

   
   drbdadm create-md linuxhandbook
                                       

   If errors occur, initialize the disk manually:

   bash Copy

   
   dd if=/dev/zero of=/dev/sdb1 bs=1024k count=1024
                                       

3. Attach Devices

   Attach the devices to the resource file:

   bash Copy

   
   drbdadm attach linuxhandbook
                                       

4. Start DRBD Service

   Enable and start the DRBD service:

   bash Copy

   
   systemctl start drbd
   systemctl enable drbd
                                       

Setting Primary and Secondary Nodes

Designate one node as the primary for read/write operations:

drbdadm primary linuxhandbook --force
                            

Verify the DRBD status:

cat /proc/drbd
                            

Using DRBD

1. Format the DRBD Device

   On the primary node, format the DRBD device:

   bash Copy

   
   mkfs -t ext3 /dev/drbd0
                                       

2. Mount the Device

   Mount the device to make it accessible:

   bash Copy

   
   mount /dev/drbd0 /mnt
                                       

3. Test Synchronization

   Create a test file on the primary node:

   bash Copy

   
   touch /mnt/drbdtest.txt
   ls /mnt/
                                       

   Promote the secondary node to primary and verify the synchronization.

Manage DRBD with LCMC

For easier management, use the Linux Cluster Management Console (LCMC) to visualize and administer DRBD clusters.

By following this guide, you can effectively set up DRBD on your CentOS systems, ensuring high availability and disaster recovery for your critical data.

Conclusion

DRBD is a robust tool for achieving high availability and disaster recovery in Linux-based systems. By mirroring block devices between two nodes, it ensures data consistency and reliability, even in cases of hardware failure. Following this guide, you can successfully set up DRBD on CentOS, making your infrastructure more resilient and reliable. Whether for failover solutions or disaster recovery planning, DRBD provides a network-based alternative to shared storage that is both efficient and secure.