[DRBD-user] drbd 8 - Failure: (104) Can not open backing device.

[Daniele Ciarelli]

Hello everybody
I have a problem configuring DRBD, my server configuration is this: 

Harddisks are configured in Raid 1 mode
Operating system: Centos5 
Kernel version: 2.6.18-8
Drbd version: 8.0.3 (api:86/proto:86)

This is my drbd.conf

resource mysql {
  protocol C;

 startup { wfc-timeout 0; degr-wfc-timeout 120; }
  disk    { on-io-error detach; }
  net     { timeout 60; connect-int 10; ping-int 10;
            max-buffers 2048; max-epoch-size 2048; }
  syncer  { rate 4M; } # sync when r0 and r1 are finished syncing.

  on server1 {
    device    /dev/drbd0;
    disk
/dev/mapper/ddf1_4035305a8680c327202020202020202028661c7b3a354a45p8;
    address   192.168.0.1:7789;
    meta-disk internal;
}

  on server2 {
    device    /dev/drbd0;
    disk
/dev/mapper/ddf1_4035305a8680c3272020202020202020b82fe21f3a354a45p3;
    address   192.168.0.2:7789;
    meta-disk internal;
}
}

The "disk" is a partition of a hard drive that was formatted with the
ext3 file system during the installation.
I tried to format this partition with ext2 but didn't succeed. This
partition is not mounted by default.

The "device" is a device file.

[root at server1 dev]# file /dev/drbd0
/dev/drbd0: block special (147/0)

When starting DRBD i receive the following error:

[root at server1 dev]# /etc/init.d/drbd start
Starting DRBD resources:    [ d0 Failure: (104) Can not open backing
device.

cmd /sbin/drbdsetup /dev/drbd0 disk
/dev/mapper/ddf1_4035305a8680c327202020202020202028661c7b3a354a45p8
/dev/mapper/ddf1_4035305a8680c327202020202020202028661c7b3a354a45p8
internal --set-defaults --create-device --on-io-error=detach  failed!

Can anyone help me with this configuration?

Thanks in advance,
Daniele