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data structure v9

Guest on 31st July 2022 01:22:35 AM

  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.

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