| ================================ | |
| 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. |