[DRBD-user] how to drbd the / filesystem device

Ben Timby btimby at gmail.com
Mon May 3 20:02:15 CEST 2010

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.


Pri/pri would only work if you use a clustered file system such as
OCFS on your root device. Probably NOT what you are looking for.

The difficulty in using DRBD on the root (of course it is possible) is
that the initial ramdisk must contain all drivers necessary for
mounting the root partition. Thus, the initrd must be able to bring up
the underlying block device, then bring up drbd, pivot to it, and then
continue the boot process. The other issue, as already mentioned is
the secondary machine. It cannot mount the drbd device as it's root
partition, thus failing over to that machine would not be easy
(possible?) without rebooting.

I think we need to know more about your boss's requirements, perhaps
you can achieve what you want. Some possibilities are:

Jack up the machine into a VM, and DRBD it's virtual HD, root replicated.

Use UnionFS along with another read only root device to provide a
read/write root device. Both systems are able to boot using just a
read only device, you then layer in a ramdisk in for writes (log files
etc) on the secondary machine. Primary machine layers DRBD for writes.
Replace that ramdisk with the DRBD device when you need to fail over.



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