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.
On all nodes:
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 kpartx -v -a /var/drbd/data_volume.dat ls /dev/mapper/ mkdir -p /mnt/drbd echo "/dev/drbd0 /mnt/drbd ext4 noauto 0 0 " >> /etc/fstab
On all nodes, configure the DRBD config in /etc/drbd.d/*conf. You may want to disable the survey.
On all nodes, configure DRBD by creating a file in /etc/drbd.d/mysql.res with:
resource mysql {
disk {
on-io-error detach;
}
device /dev/drbd0;
disk /dev/mapper/loop0p1;
meta-disk internal;
on $hostname {
address 172.20.10.10:7700;
}
on $hostname {
address 172.20.10.9:7700;
}
}
TODO: Can you just use /dev/loop0 instead?!
Be sure to rename the hostnames so that it matches the actual machine's hostname. Otherwise, when you try creating the resource, you will get an error like:
'mysql' not defined in your config (for this host).
On all nodes, create the resource:
drbdadm -v create-md mysql
If it complains about finding a filesystem, zero out the first few blocks using dd and try again.
On all nodes, start the resource:
drbdadm up mysql
On one of the nodes, force it to be the primary node for the resource:
drbdadm -- --force primary mysql
On the primary node, create a file system:
mkfs -t xfs /dev/drbd0
On the primary node, set it back to a secondary node:
drbadm secondary mysql
On all the nodes, verify the role. They should all be Secondary/Secondary.
drbadm role mysql
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