Setting up DRBD on an active MySQL server
Unfortunately, it is not possible to do either one.

Once you create /dev/drbd0 on both DB Servers, you have to mount the DRBD Primary on a folder. That folder cannot have anything with active file handles. The protocol I use is:

drbdadm primary drbd0
mount /dev/drbd0 /var/lib/mysql
service mysql start


You want DRBD to house MySQL Data. Here is what you must do instead

service mysql stop
mv /var/lib/mysql /var/lib/mysql_old
mkdir /var/lib/mysql
chown mysql:mysql /var/lib/mysql
drbdadm primary drbd0
mount /dev/drbd0 /var/lib/mysql
cp -R /var/lib/mysql_old /var/lib/mysql
chown -R mysql:mysql /var/lib/mysql
service mysql start


As shown, stopping mysqld is mandatory.

UPDATE 2013-03-16 21:46 EDT

There is something incredibly tough you can try


Given ServerDB1 with MySQL Running
Given ServerDB2 to introduce as DRBD partner


STEP 01) Setup DRBD on Separate ServerDB2

As I mentioned earlier, you can house mysql on a DRBD mount.

STEP 02) Setup MySQL Replication

Huh ??? How did MySQL Replication enter the picture


You need to mysqldump everything in ServerDB1
Load the mysqldump into MySQL running in ServerDB2
Setup Replication so all changes are migrated since loading of ServerDB2 was done


STEP 03) Failover Your Application

In simple English, use the IP address of ServerDB2 in your application instead of ServerDB1

You should wait and make sure you have a low peak time to do this failover

STEP 04) Setup DRBD on Separate ServerDB1


Setup DRBD
drbdadm secondary drbd0
drbdadm coonect drbd0


This is an oversimplified description but you can look up the actual code to sync a DRBD pair

Here is my old DRBD download-and-install script

DRBD_VERSION=8.3
DRBD_SUBVERSION=0
DRBD_VERSION_NUMBER=${DRBD_VERSION}.${DRBD_SUBVERSION}
cd
rm -rf drbdinstall
mkdir drbdinstall
cd drbdinstall
wget http://oss.linbit.com/drbd/${DRBD_VERSION}/drbd-${DRBD_VERSION_NUMBER}.tar.gz
gzip -d drbd-${DRBD_VERSION_NUMBER}.tar.gz
tar -xvf drbd-${DRBD_VERSION_NUMBER}.tar
cd drbd-${DRBD_VERSION_NUMBER}
make rpm
rpm -Uvh dist/RPMS/x86_64/drbd-*


You can go to www.drbd.org to find out the latest version number and update the aforemtioned script

Give it a Try !!!