From d81dc4f45b0aaa7e02adc01a9a12dfd9b9d36bba Mon Sep 17 00:00:00 2001 From: Andreas Gruenbacher Date: Fri, 10 Jun 2011 17:02:53 +0200 Subject: [PATCH] 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 Signed-off-by: Philipp Reisner --- .../blockdev/drbd/data-structure-v9.txt | 38 +++++++++++++++++++ 1 file changed, 38 insertions(+) create mode 100644 Documentation/blockdev/drbd/data-structure-v9.txt diff --git a/Documentation/blockdev/drbd/data-structure-v9.txt b/Documentation/blockdev/drbd/data-structure-v9.txt new file mode 100644 index 000000000000..1e52a0e32624 --- /dev/null +++ b/Documentation/blockdev/drbd/data-structure-v9.txt @@ -0,0 +1,38 @@ +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.