Running a DRBD resource in dual-primary mode is a mandatory requirement for using GFS2 with the resource. It is advisable not to underestimate the risks that emanate from this kind of DRBD use.

Standard Filesystems

Filesystems exist for a good reason: They make memory space manageable. Without a filesystem, it would be difficult to find data that you write to the storage medium when you need it. The filesystem structure makes it possible to retrieve and modify content on the storage medium. As long as nothing gets in the filesystem's way, this principle works well. And, as long as a storage medium is consistent, everything is well in the admin's universe.

Filesystems always assume that they are the only entity allowed to access a storage medium – or, to be more precise, that only the filesystem instance that belongs to a specific mount is allowed to do so. Simultaneous access by two filesystems to the same storage medium is not included in the concept of the standard filesystem on Linux. The filesystems in Linux thus go to great lengths to prevent simultaneous access by two or more instances of a filesystem to the same medium. You can't remount a filesystem at a different position if it is already