Prerequisites

- Setup Minimal CentOS 5

- be sure that both nodes can resolve correctly names (either through dns or /etc/hosts)

- yum update (as usual ...)

- yum install heartbeat drbd kmod-drbd (available in the extras repository)

People wanting to use drbd 8.2.6 instead of 8.0.13 have to use drbd82 and kmod-drbd82 . Please keep in mind that you can't mix versions. Configuration syntax is also different

Current situation :

• node1.yourdomain.org 172.29.156.20/24 , source disc /dev/sdb that will be replicated
• node2.yourdomain.org 172.29.156.21/24 , target disc /dev/sdb

DRBD Configuration

We'll configure DRBD so that /dev/sdb will be replicated from one node to the other (roles can be changed at any time though) The name of the drbd resource will be "repdata" (you can of course use the name you want). Here is the content of the /etc/drbd.conf file :

    #
    # please have a a look at the example configuration file in
    # /usr/share/doc/drbd/drbd.conf
    #
    global { usage-count no; }
    resource repdata {
       protocol C;
       startup { wfc-timeout 0; degr-wfc-timeout     120; }
       disk { on-io-error detach; } # or panic, ...
       net {  cram-hmac-alg "sha1"; shared-secret "Cent0Sru!3z"; } # don't forget to choose a secret for auth !
       syncer { rate 10M; }
       on node1.yourdomain.org {
         device /dev/drbd0;
         disk /dev/sdb;
         address 172.29.156.20:7788;
         meta-disk internal;
    }
    on node2.yourdomain.org {
         device /dev/drbd0;
         disk /dev/sdb;
         address 172.29.156.21:7788;
         meta-disk internal;
       }
    }

- replicate this config file (/etc/drbd.conf) to the second node

    # scp /etc/drbd.conf root@node2:/etc/

Initialize the meta-data area on disk before starting drbd (! on both nodes!)

    [root@node1 etc]# drbdadm create-md repdata
    v08 Magic number not found
    v07 Magic number not found
    About to create a new drbd meta data block on /dev/sdb.
       ==> This might destroy existing data! <==
    Do you want to proceed? [need to type 'yes' to confirm] yes
    Creating meta data... initialising activity log NOT initialized bitmap (256 KB) New drbd meta data block sucessfully created.

- start drbd on both nodes (service drbd start)

    [root@node1 etc]# service drbd start
    Starting DRBD resources:    [ d0 n0 ]. ......

    [root@node1 etc]# cat /proc/drbd
     version: 8.0.4 (api:86/proto:86) SVN Revision: 2947 build by buildsvn@c5-i386-build, 2007-07-31 19:17:18
      0: cs:Connected st:Secondary/Secondary ds:Inconsistent/Inconsistent C r---
       ns:0 nr:0 dw:0 dr:0 al:0 bm:0 lo:0 pe:0 ua:0 ap:0
       resync: used:0/31 hits:0 misses:0 starving:0 dirty:0 changed:0 act_log: used:0/257 hits:0 misses:0 starving:0 dirty:0 changed:0

    [root@node1 etc]# ssh root@node2 cat /proc/drbd  
     version: 8.0.4 (api:86/proto:86) SVN Revision: 2947 build by buildsvn@c5-i386-build, 2007-07-31 19:17:18
      0: cs:Connected st:Secondary/Secondary ds:Inconsistent/Inconsistent C r---
       ns:0 nr:0 dw:0 dr:0 al:0 bm:0 lo:0 pe:0 ua:0 ap:0
       resync: used:0/31 hits:0 misses:0 starving:0 dirty:0 changed:0 act_log: used:0/257 hits:0 misses:0 starving:0 dirty:0 changed:

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 :

    [root@node1 etc]# drbdadm -- --overwrite-data-of-peer primary repdata
    [root@node1 etc]# watch -n 1 cat /proc/drbd  
    version: 8.0.4 (api:86/proto:86) SVN Revision: 2947 build by buildsvn@c5-i386-build, 2007-07-31 19:17:18
     0: cs:SyncTarget st:Primary/Secondary ds:Inconsistent/Inconsistent C r---
       ns:0 nr:68608 dw:68608 dr:0 al:0 bm:4 lo:0 pe:0 ua:0 ap:0
         [>...................] sync'ed:  0.9% (8124/8191)M finish: 0:12:05 speed: 11,432 (11,432) K/sec 
       resync: used:0/31 hits:4283 misses:5 starving:0 dirty:0 changed:5 act_log: used:0/257 hits:0 misses:0 starving:0 dirty:0 changed:0

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

    [root@node1]# mkfs.ext3 /dev/drbd0 ; mkdir /repdata ; mount /dev/drbd0 /repdata

- create some fake data on node 1 :

    [root@node1 etc]# for i in {1..5};do dd if=/dev/zero of=/repdata/file$i bs=1M count=100;done

- now switch manually to the second node :

    [root@node1 /]# umount /repdata ; drbdadm secondary repdata
    [root@node2 /]# mkdir /repdata ; drbdadm primary repdata ; mount /dev/drbd0 /repdata
    [root@node2 /]# ls /repdata/ file1  file2  file3  file4  file5  lost+found

Great, data was replicated .... now let's delete/add some file :

    [root@node2 /]# rm /repdata/file2 ; dd if=/dev/zero of=/repdata/file6 bs=100M count=2

- Now switch back to the first node :

    [root@node2 /]# umount /repdata/ ; drbdadm secondary repdata
    [root@node1 /]# drbdadm primary repdata ; mount /dev/drbd0 /repdata
    [root@node1 /]# ls /repdata/ file1  file3  file4  file5  file6  lost+found

OK ... Drbd is working ... let's be sure that it will always be started :

    # chkconfig drbd on

Heartbeat V2 Configuration

Let's configure a simple /etc/ha.d/ha.cf file :

    logfile    /var/log/ha-log
    logfacility    local0
    keepalive 2
    deadtime 6
    initdead 120
    udpport    694
    ucast eth0 172.29.156.21
    auto_failback on
    node node1 node2
    respawn hacluster /usr/lib64/heartbeat/ipfail
    ping 172.29.156.1

Create also the /etc/ha.d/authkeys (with permissions 600 !!!) :

    auth 2
    2 sha1 MyPassword

Start the heartbeat service on node1 :

    [root@node1 ha.d]# service heartbeat start
    Starting High-Availability services: [OK]

Replicate now the ha.cf and authkeys to node2 and start heartbeat

    [root@node1 ha.d]# scp /etc/ha.d/ha.cf /etc/ha.d/authkeys root@node2:/etc/ha.d/
    [root@node2 ha.d]# service heartbeat start

Firewall considerations

You will need to make sure that the nodes can talk on ports:

    DRBD: 7788
    HEARTBEAT: 694

Ref:
http://wiki.centos.org/HowTos/Ha-Drbd