Andreas Gruenbacher | d81dc4f | 2011-06-10 17:02:53 +0200 | [diff] [blame] | 1 | This describes the in kernel data structure for DRBD-9. Starting with |
| 2 | Linux v3.14 we are reorganizing DRBD to use this data structure. |
| 3 | |
| 4 | Basic Data Structure |
| 5 | ==================== |
| 6 | |
| 7 | A node has a number of DRBD resources. Each such resource has a number of |
| 8 | devices (aka volumes) and connections to other nodes ("peer nodes"). Each DRBD |
| 9 | device is represented by a block device locally. |
| 10 | |
| 11 | The DRBD objects are interconnected to form a matrix as depicted below; a |
| 12 | drbd_peer_device object sits at each intersection between a drbd_device and a |
| 13 | drbd_connection: |
| 14 | |
| 15 | /--------------+---------------+.....+---------------\ |
| 16 | | resource | device | | device | |
| 17 | +--------------+---------------+.....+---------------+ |
| 18 | | connection | peer_device | | peer_device | |
| 19 | +--------------+---------------+.....+---------------+ |
| 20 | : : : : : |
| 21 | : : : : : |
| 22 | +--------------+---------------+.....+---------------+ |
| 23 | | connection | peer_device | | peer_device | |
| 24 | \--------------+---------------+.....+---------------/ |
| 25 | |
| 26 | In this table, horizontally, devices can be accessed from resources by their |
| 27 | volume number. Likewise, peer_devices can be accessed from connections by |
| 28 | their volume number. Objects in the vertical direction are connected by double |
| 29 | linked lists. There are back pointers from peer_devices to their connections a |
| 30 | devices, and from connections and devices to their resource. |
| 31 | |
| 32 | All resources are in the drbd_resources double-linked list. In addition, all |
| 33 | devices can be accessed by their minor device number via the drbd_devices idr. |
| 34 | |
| 35 | The drbd_resource, drbd_connection, and drbd_device objects are reference |
| 36 | counted. The peer_device objects only serve to establish the links between |
| 37 | devices and connections; their lifetime is determined by the lifetime of the |
| 38 | device and connection which they reference. |