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1================================2kernel data structure for DRBD-93================================4 5This describes the in kernel data structure for DRBD-9. Starting with6Linux v3.14 we are reorganizing DRBD to use this data structure.7 8Basic Data Structure9====================10 11A node has a number of DRBD resources. Each such resource has a number of12devices (aka volumes) and connections to other nodes ("peer nodes"). Each DRBD13device is represented by a block device locally.14 15The DRBD objects are interconnected to form a matrix as depicted below; a16drbd_peer_device object sits at each intersection between a drbd_device and a17drbd_connection::18 19 /--------------+---------------+.....+---------------\20 | resource | device | | device |21 +--------------+---------------+.....+---------------+22 | connection | peer_device | | peer_device |23 +--------------+---------------+.....+---------------+24 : : : : :25 : : : : :26 +--------------+---------------+.....+---------------+27 | connection | peer_device | | peer_device |28 \--------------+---------------+.....+---------------/29 30In this table, horizontally, devices can be accessed from resources by their31volume number. Likewise, peer_devices can be accessed from connections by32their volume number. Objects in the vertical direction are connected by double33linked lists. There are back pointers from peer_devices to their connections a34devices, and from connections and devices to their resource.35 36All resources are in the drbd_resources double-linked list. In addition, all37devices can be accessed by their minor device number via the drbd_devices idr.38 39The drbd_resource, drbd_connection, and drbd_device objects are reference40counted. The peer_device objects only serve to establish the links between41devices and connections; their lifetime is determined by the lifetime of the42device and connection which they reference.43