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! >From the drbd9 documentation I read that this behavior should be normal: https://docs.linbit.com/docs/users-guide-9.0/ "11.3. Manual split brain recovery" If DRBD detects that both nodes are (or were at some point, while disconnected) in the primary role, it immediately tears down the replication connection. The tell-tale sign of this is a message like the following appearing in the system log: Split-Brain detected, dropping connection! The solution for this problem is to use "drbdadm --discard-my-data connect res" on the node2 that made the backup. But my Question is why do I *sometimes not* have a split brain ? It does not make a difference if I write to or read from the primary device while the backup is running.
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