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