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authorAndreas Gruenbacher <agruen@linbit.com>2011-06-10 17:02:53 +0200
committerPhilipp Reisner <philipp.reisner@linbit.com>2014-02-17 16:27:48 +0100
commitd81dc4f45b0aaa7e02adc01a9a12dfd9b9d36bba (patch)
tree9e957b1f1b627ad0d704e06a54b5a1aae218eb70 /Documentation/blockdev
parent05f7a7d6a7d23a877063857cf2df1dffec5a96dc (diff)
drbd: Describe the future high-level structure of DRBD
The following commits will successively transform DRBD into the structure described here. Signed-off-by: Andreas Gruenbacher <agruen@linbit.com> Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Diffstat (limited to 'Documentation/blockdev')
-rw-r--r--Documentation/blockdev/drbd/data-structure-v9.txt38
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+This describes the in kernel data structure for DRBD-9. Starting with
+Linux v3.14 we are reorganizing DRBD to use this data structure.
+
+Basic Data Structure
+====================
+
+A node has a number of DRBD resources. Each such resource has a number of
+devices (aka volumes) and connections to other nodes ("peer nodes"). Each DRBD
+device is represented by a block device locally.
+
+The DRBD objects are interconnected to form a matrix as depicted below; a
+drbd_peer_device object sits at each intersection between a drbd_device and a
+drbd_connection:
+
+ /--------------+---------------+.....+---------------\
+ | resource | device | | device |
+ +--------------+---------------+.....+---------------+
+ | connection | peer_device | | peer_device |
+ +--------------+---------------+.....+---------------+
+ : : : : :
+ : : : : :
+ +--------------+---------------+.....+---------------+
+ | connection | peer_device | | peer_device |
+ \--------------+---------------+.....+---------------/
+
+In this table, horizontally, devices can be accessed from resources by their
+volume number. Likewise, peer_devices can be accessed from connections by
+their volume number. Objects in the vertical direction are connected by double
+linked lists. There are back pointers from peer_devices to their connections a
+devices, and from connections and devices to their resource.
+
+All resources are in the drbd_resources double-linked list. In addition, all
+devices can be accessed by their minor device number via the drbd_devices idr.
+
+The drbd_resource, drbd_connection, and drbd_device objects are reference
+counted. The peer_device objects only serve to establish the links between
+devices and connections; their lifetime is determined by the lifetime of the
+device and connection which they reference.

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