DRBD 8.4 on Debian Jessie

From  www.linbit.com:

"The Distributed Replicated Block Device (DRBD) is a software-based, shared-nothing, replicated storage solution mirroring the content of block devices (hard disks, partitions, logical volumes etc.) between hosts.

DRBD mirrors data

• in real time. Replication occurs continuously while applications modify the data on the device.
• transparently. Applications need not be aware that the data is stored on multiple hosts.
• synchronously or asynchronously. With synchronous mirroring, applications are notified of write completions after the writes have been carried out on all hosts. With asynchronous mirroring, applications are notified of write completions when the writes have completed locally, which usually is before they have propagated to the other hosts."
  

Lets go and prepare two nodes d01 and d02

During linux nodes installation we must setup IP, hostame and domain name.

d01.xxx.local    192.168.50.131
d02.xxx.local    192.168.50.132

Install on both nodes:

#apt-get install ntpdate
#service ntp restart
# apt-get install drbd8-utils
# modprobe drbd

Test:

 # lsmod | grep drbd
drbd                  193312  0
lru_cache               5042  1 drbd
cn                      4563  1 drbd

Clear config and configure on both nodes:

 # :> /etc/drbd.conf 
# nano /etc/drbd.conf

global { usage-count no; }
common {
disk {
        on-io-error detach;
        no-disk-flushes;
        no-disk-barrier;
        c-plan-ahead 10;
        c-fill-target 24M;
        c-min-rate 10M;
        c-max-rate 700M;
}
}
resource r0 {
        protocol C;
        startup {
                wfc-timeout  15;
                degr-wfc-timeout 60;
        }
        net {
                max-buffers             36k;
                sndbuf-size            1024k ;
                rcvbuf-size            2048k;
#                cram-hmac-alg sha1;
#                shared-secret "enteryoursharedsecret";
        }
        on d01 {       #important - dont use domain name here only short hostname
                device /dev/drbd0;
                disk /dev/sdb1;
                address 192.168.50.131:7788;
                meta-disk internal;
        }
        on d02 {     #important - dont use domain name here only short hostname
                device /dev/drbd0;
                disk /dev/sdb1;
                address 192.168.50.132:7788;
                meta-disk internal;
        }
}

Enable resourceon both nodes

# /etc/init.d/drbd start
# drbdadm create-md r0
# drbdadm up r0

Setup primary node

# drbdadm primary --force r0 
  

Check sync

# watch cat /proc/drbd

After full sync make fs and mount it to directory

# mkfs.ext3 /dev/drbd0
# mkdir /data
# mount /dev/drbd0 /data

Test if is mounted

# df -h

udev            2,0G     0  2,0G   0% /dev
tmpfs           396M  5,5M  391M   2% /run
/dev/sda1        12G 1006M   11G   9% /
tmpfs           2,0G     0  2,0G   0% /dev/shm
tmpfs           5,0M     0  5,0M   0% /run/lock
tmpfs           2,0G     0  2,0G   0% /sys/fs/cgroup
tmpfs           396M     0  396M   0% /run/user/1000
/dev/drbd0      243G   61M  230G   1% /data

TEST after failure

Create some files 
on d01

# touch /data/alfa.txt
#touch /data/beta.txt

unmount it and promote d01 to secondary

#umount /data
# drbdadm secondary r0

promote d02 to primary and mount data
on d02:
# drbdadm primary r0
# mkdir /data
# mount /dev/drbd0 /data

Now you should see your files here

# ls /data
 alfa.txt  beta.txt  lost+found

THATS ALL :)