This based on my last post where I documented building a Highly Available NFS/NAS server.

There is not a huge amount that needs to be done in order to add iSCSI functionality as well.

Add a file called /etc/drbd/iscsi.res containing:

resource iscsi {
    on nfs1 {
        device /dev/drbd1;
        disk   /dev/vdc;
        meta-disk internal;
        address   10.0.0.1:7789;
    }
    on nfs2 {
        device /dev/drbd1;
        disk   /dev/vdc;
        meta-disk internal;
        address   10.0.0.2:7789;
    }
}

This differs from the previous resource in 2 ways. Obviously it using a different physical disk. Also the port number of the address is incremented; each resource has to have its own port to communicate on.

Take 2 Centos Servers (nfs1 and nfs2 will do nicely) and install ELrepo and EPEL on them both:

yum install \
    https://download.fedoraproject.org/pub/epel/6/i386/epel-release-6-5.noarch.rpm \
    https://elrepo.org/elrepo-release-6-4.el6.elrepo.noarch.rpm --nogpgcheck

Each of them should ideally have 2 NICS, with the secondary ones just used for DRBD sync purposes. We’ll give these the address 10.0.0.1/32 and 10.0.0.2/32.

I am also assuming that you have disabled the firewall and SELinux – I do not recommend that for production, but for testing it is fine.