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d81dc4f4 AG |
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. |