1================================ 2kernel data structure for DRBD-9 3================================ 4 5This describes the in kernel data structure for DRBD-9. Starting with 6Linux v3.14 we are reorganizing DRBD to use this data structure. 7 8Basic Data Structure 9==================== 10 11A node has a number of DRBD resources. Each such resource has a number of 12devices (aka volumes) and connections to other nodes ("peer nodes"). Each DRBD 13device is represented by a block device locally. 14 15The DRBD objects are interconnected to form a matrix as depicted below; a 16drbd_peer_device object sits at each intersection between a drbd_device and a 17drbd_connection:: 18 19 /--------------+---------------+.....+---------------\ 20 | resource | device | | device | 21 +--------------+---------------+.....+---------------+ 22 | connection | peer_device | | peer_device | 23 +--------------+---------------+.....+---------------+ 24 : : : : : 25 : : : : : 26 +--------------+---------------+.....+---------------+ 27 | connection | peer_device | | peer_device | 28 \--------------+---------------+.....+---------------/ 29 30In this table, horizontally, devices can be accessed from resources by their 31volume number. Likewise, peer_devices can be accessed from connections by 32their volume number. Objects in the vertical direction are connected by double 33linked lists. There are back pointers from peer_devices to their connections a 34devices, and from connections and devices to their resource. 35 36All resources are in the drbd_resources double-linked list. In addition, all 37devices can be accessed by their minor device number via the drbd_devices idr. 38 39The drbd_resource, drbd_connection, and drbd_device objects are reference 40counted. The peer_device objects only serve to establish the links between 41devices and connections; their lifetime is determined by the lifetime of the 42device and connection which they reference. 43