[DRBD-user] DRBD9 disconnect, double primary -> connect again -> Sometimes "initial Split Brain", sometimes not

[Jochen Kamuf]

Hi,

I have two identical bare metal machines "server1" and "server2" running
DRBD_KERNEL_VERSION=9.0.13 on Opensuse Leap15.
I have one resource "res1"

Double Primary is NOT allowed.

If I run the following scenario:

0. "server1" stops the VM that uses the res1 for the virtual hard disk
(to ensure a consistent vm state of the backup and have no read/writes
on the drbd resource )

1. Set "res1" on both nodes "server1" and "server2" to secondary and
disconnect
2. Set "res1" on both nodes to primary in standalone mode
3. "server1" starts the VM that uses the res1 for the virtual hard disk
4. "server2"  run the command "ddrescue /dev/drbd/by-res/bb
/backup/backup.img"

5. When the backup is finished I set "res1" on node"server2" to
secondary ( while on server1 the res1 is already on primary and gets
reads/writes )
6. Connect both nodes again

Now I have a "random" behavior:

Sometimes the res1 is connected after I run the command "drbdadm connect
res1" on both nodes.

Sometimes I become:

server1 :~  #drbdadm status res1:

server1 role:Primary
  disk:UpToDate
  server2 connection:StandAlone

And If I look into the log file on server1 :

drbd res1/0 drbd1: Split-Brain detected but unresolved, dropping connection!