Installation

Centos 7

rpm --import https://www.elrepo.org/RPM-GPG-KEY-elrepo.org
rpm -Uvh http://www.elrepo.org/elrepo-release-7.0-2.el7.elrepo.noarch.rpm 
yum -y install drbd84-utils kmod-drbd84

Centos 6

rpm --import http://elrepo.org/RPM-GPG-KEY-elrepo.org
rpm -Uvh http://elrepo.org/elrepo-release-6-5.el6.elrepo.noarch.rpm
rpm -Uvh http://download.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm
rpm --import 'http://keys.gnupg.net:11371/pks/lookup?search=0x0608B895&op=get'
yum -y install drbd84-utils kmod-drbd84

Configuration

create /etc/drbd.d/drbd1.res

resource repdata {
  protocol C;
  startup { wfc-timeout 60; degr-wfc-timeout     120; }
  disk {
        c-fill-target 1M;
        c-max-rate 1M;
        resync-rate 1M; 
        on-io-error detach; } # or panic, ...
# set a shared password  
net {  cram-hmac-alg "sha1"; shared-secret "ent0Sru!3zMi2fwf12fi"; } 

#the names server1 and server2 must be the fqdn of the servers - case sensitive!    
  on server1 {
    device /dev/drbd0;
    # this is the dev that you are going to create the mirror on
    # it could be a partition or a logical drive
    disk /dev/vda3;
    #this is the ip address of server1 and the port used for replication
    # make sure you permit this port through iptables!
    address 10.254.253.52:7788;
    meta-disk internal;
  }
  on server2 {
    device /dev/drbd0;
    disk /dev/vda3;
    #this is the ip address of server2 and the port used for replication
    address 10.254.253.53:7788;
    meta-disk internal;
  }
}

fdisk /dev/vda and create the correct partitions needed

 drbdadm create-md repdata

You should get the message:

New drbd meta data block successfully created.

If you get an error message that includes:

Device size would be truncated, which
would corrupt data and result in
'access beyond end of device' errors.
You need to either
   * use external meta data (recommended)
   * shrink that filesystem first
   * zero out the device (destroy the filesystem)
Operation refused.

The partition is probably already formatted. Clear the formatting with :

 dd if=/dev/zero of=/dev/XXXX bs=1M count=128

Replace XXXX above with the correct device, such as vda2 or mapper/vg_drbd1-lv_opt

start drbd on both nodes (service drbd start)

service drbd start
cat /proc/drbd

As you can see , both nodes are secondary, which is normal. we need to decide which node will act as a primary now (node1) : that will initiate the first ‘full sync’ between the two nodes :

drbdadm -- --overwrite-data-of-peer primary repdata

Monitor the status:

watch -n 1 cat /proc/drbd

we can now format /dev/drbd0 and mount it on node1 :

 mkfs.ext3 /dev/drbd0 ; mkdir /repdata ; mount /dev/drbd0 /repdata

Outdated/DUnknown

If you cat /proc/drbd and get:

0: cs:WFConnection ro:Secondary/Unknown ds:Outdated/DUnknown C r-----

On the primary node, execute

drbdadm connect all

and if needed, on the secondary node, execute

drbdadm -- --discard-my-data connect all

References

SNMP

http://lists.linbit.com/pipermail/drbd-user/2007-November/007780.html