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- ================================
- kernel data structure for DRBD-9
- ================================
- 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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