DRBD

DRBD (Distributed Replicated Block Device) is a virtual block device that is distributed across two or more machines.

Installation

On a clean installation of RHEL 7 or equivalent, run updates, and ensure that you have NTP and a recent kernel installed.

From ElRepo

Get the DRBD packages from ELRepo:

rpm -Uvh http://www.elrepo.org/elrepo-release-7.0-2.el7.elrepo.noarch.rpm
yum install drbd84-utils kmod-drbd84

From Source

Install prerequisites:

yum install gcc flex make autoconf m4

Get the source from their git repository. Releases from tarballs may fail depending on which kernel version you're using.

git clone git://git.drbd.org/drbd-8.4.git
cd drbd-8.4
make
make install

The make install should have loaded the module and you can verify this:

lsmod | grep drbd

If it isn't loaded, load it using modprobe

modprobe drbd

Compile the userspace utilities:

git clone git://git.drbd.org/drbd-utils.git
cd drbd-utils
./aclocal.sh
./configure --prefix=/usr --localstatedir=/var --sysconfdir=/etc
make
make install

Note: I got errors about man pages not being found. Ugh.

Configuration

This section will configure DRBD for use in a redundant MySQL setup.

DRBD syncs volumes. If you did not configure a partition or have a separate disk to mirror, you can create a file volume instead.

mkdir /var/drbd
cd /var/drbd

# Create a 50GB volume
dd if=/dev/zero of=data_volume.dat bs=1024 count=52428800

# Create a partition
fdisk data_volume.dat

# Create a device
losetup /dev/loop0 /var/drbd/data_volume.dat

mkdir -p /mnt/drbd
echo "/dev/drbd0 /mnt/drbd ext4 noauto 0 0 " >>  /etc/fstab

Configure DRBD by creating a file in /etc/drbd.d/mysql.res

resource mysql {
  device    "/dev/brdb0";
  disk      "/dev/loop0";
  meta-disk internal;
  on node1 {
    address ipv4 10.0.42.100:7700;
  }
  on node2 {
    address ipv4 10.0.42.254:7700;
  }
}

See Also

• https://drbd.linbit.com/users-guide/s-build-from-source.html
• http://unix-linux-server.blogspot.ca/2014/10/drbd-on-centos-70-oracle-linux-70-and.html
• http://wiki.centos.org/HowTos/Ha-Drbd (CentOS 5)
• http://wiki.openvz.org/HA_cluster_with_DRBD_and_Heartbeat