This feature is available in DRBD 8.0 and later.
In dual-primary mode, any resource is, at any given time, in the primary role on both cluster nodes. Since concurrent access to the data is thus possible, this mode requires the use of a shared cluster file system that utilizes a distributed lock manager. Examples include GFS and OCFS2.
Deploying DRBD in dual-primary mode is the preferred approach for load-balancing clusters which require concurrent data access from two nodes. This mode is disabled by default, and must be enabled explicitly in DRBD's configuration file.
See the section called “Enabling dual-primary mode” for information on enabling dual-primary mode for specific resources.