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