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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>
authored by
Andreas Gruenbacher
and committed by
Philipp Reisner
d81dc4f4
05f7a7d6
+38
+38
Documentation/blockdev/drbd/data-structure-v9.txt
+38
Documentation/blockdev/drbd/data-structure-v9.txt
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This describes the in kernel data structure for DRBD-9. Starting with
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Linux v3.14 we are reorganizing DRBD to use this data structure.
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Basic Data Structure
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====================
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A node has a number of DRBD resources. Each such resource has a number of
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devices (aka volumes) and connections to other nodes ("peer nodes"). Each DRBD
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device is represented by a block device locally.
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The DRBD objects are interconnected to form a matrix as depicted below; a
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drbd_peer_device object sits at each intersection between a drbd_device and a
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drbd_connection:
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/--------------+---------------+.....+---------------\
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| resource | device | | device |
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+--------------+---------------+.....+---------------+
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| connection | peer_device | | peer_device |
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+--------------+---------------+.....+---------------+
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: : : : :
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: : : : :
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+--------------+---------------+.....+---------------+
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| connection | peer_device | | peer_device |
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\--------------+---------------+.....+---------------/
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In this table, horizontally, devices can be accessed from resources by their
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volume number. Likewise, peer_devices can be accessed from connections by
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their volume number. Objects in the vertical direction are connected by double
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linked lists. There are back pointers from peer_devices to their connections a
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devices, and from connections and devices to their resource.
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All resources are in the drbd_resources double-linked list. In addition, all
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devices can be accessed by their minor device number via the drbd_devices idr.
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The drbd_resource, drbd_connection, and drbd_device objects are reference
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counted. The peer_device objects only serve to establish the links between
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devices and connections; their lifetime is determined by the lifetime of the
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device and connection which they reference.