| ================================ |
| kernel data structure for DRBD-9 |
| ================================ |
| |
| This describes the in kernel data structure for DRBD-9. Starting with |
| Linux v3.14 we are reorganizing DRBD to use this data structure. |
| |
| Basic Data Structure |
| ==================== |
| |
| A node has a number of DRBD resources. Each such resource has a number of |
| devices (aka volumes) and connections to other nodes ("peer nodes"). Each DRBD |
| device is represented by a block device locally. |
| |
| The DRBD objects are interconnected to form a matrix as depicted below; a |
| drbd_peer_device object sits at each intersection between a drbd_device and a |
| drbd_connection:: |
| |
| /--------------+---------------+.....+---------------\ |
| | resource | device | | device | |
| +--------------+---------------+.....+---------------+ |
| | connection | peer_device | | peer_device | |
| +--------------+---------------+.....+---------------+ |
| : : : : : |
| : : : : : |
| +--------------+---------------+.....+---------------+ |
| | connection | peer_device | | peer_device | |
| \--------------+---------------+.....+---------------/ |
| |
| In this table, horizontally, devices can be accessed from resources by their |
| volume number. Likewise, peer_devices can be accessed from connections by |
| their volume number. Objects in the vertical direction are connected by double |
| linked lists. There are back pointers from peer_devices to their connections a |
| devices, and from connections and devices to their resource. |
| |
| All resources are in the drbd_resources double-linked list. In addition, all |
| devices can be accessed by their minor device number via the drbd_devices idr. |
| |
| The drbd_resource, drbd_connection, and drbd_device objects are reference |
| counted. The peer_device objects only serve to establish the links between |
| devices and connections; their lifetime is determined by the lifetime of the |
| device and connection which they reference. |
