Trouble shooting guide

Mirroring is not working

You have mounted the filesystem on drbd on the primary and in read-only mode on the secondary. If you modify the filesystem on the primary, the secondary is not reflecting all the changes!

Please read the first two paragraphs of the user manual again.
In other words: It is not possible to mount one filesystem on two nodes concurrently.
The way to go: The standby node only mounts the filesystem while the mast is down!

Unresolved symbols

When loading the module you see about 50 messages like these:

drbd.o: unresolved symbol sock_alloc
drbd.o: unresolved symbol proc_register
drbd.o: unresolved symbol schedule_timeout
...

Your Kernel was built with CONFIG_MODVERSIONS and the DRBD module was built without MODVERSIONS, or vice versa.

There are two ways to solve this:

• Use a system without MODVERSIONS:
  Change your kernel configuration and drop the CONFIG_MODVERSIONS option. (See ~linux/.config.) Rebuild the kernel.
• Use a system with MODVERSIONS:
  Edit ~drbd/Makefile.vars and add -DMODVERSIONS -DCONFIG_MODVERSIONS to KERNFLAGS. Rebuild DRBD.

Timeouts

During heavy load you will find messages like the following in your syslog:

...
drbd0: ack timeout detected!
drbd0: Connection lost.
drbd0: Connection established.
...

You should increase the timeout values, until you do not experience any timeouts unless you cut a cable. On the other hand, if the connection is interrupted, the application writing to the DRBD device may be blocked until the interruption is detected, which may last as long as the timeout is. (This is also the case for applications writing to the device via a filesystem)