openstack/cinder
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Updates overprovisioning dev-ref

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Updates the overprovisioning dev-ref with the correct definitions and
terminology related to thin provisioning. Drivers maintiners
implementing thin provisioning should follow these guidelines.

Change-Id: Ief540d3e924075450a0cf42f76878521587bf3dd
Signed-off-by: Gorka Eguileor <geguileo@redhat.com>
Implements: bp provisioning-improvements
This commit is contained in:
Erlon R. Cruz 2018-01-29 15:35:56 -02:00
parent 6ab3fb6b3a
commit e3cdd6b8c8
2 changed files with 52 additions and 0 deletions
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1
doc/source/contributor/index.rst
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@ -58,6 +58,7 @@ Background Concepts for Cinder
architecture
attach_detach_conventions
attach_detach_conventions_v2
thin_provisioning
threading
i18n
rpc

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doc/source/contributor/thin_provisioning.rst Normal file
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@ -0,0 +1,51 @@
Cinder Thin provisioning and Oversubscription
==============================================
Background
~~~~~~~~~~
After the support on Cinder for Thin provisioning, driver maintainers have
been struggling to understand what is the expected behavior of their drivers
and what exactly each value reported means. This document summarizes the
concepts, definitions and terminology from all specs related to the subject
and should be used as reference for new drivers implementing support for thin
provisioning.
Core concepts and terminology
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In order to maintain the same behavior among all drivers, we first need to
define some concepts used throughout drivers. This terminology is discussed
and defined in this spec[1] and should be used as reference in further
implementations.
Stats to be reported
~~~~~~~~~~~~~~~~~~~~
The following fields should be reported by drivers supporting thin
provisioning on the get_volume_stats() function:
Mandatory Fields
----------------
.. code-block:: ini
thin_provisioning_support = True (or False)
Optional Fields
---------------
.. code-block:: ini
thick_provisioning_support = True (or False)
provisioned_capacity_gb = PROVISIONED_CAPACITY
max_over_subscription_ratio = MAX_RATIO
.. note::
If provisioned_capacity_gb is not reported, the value used in the scheduler
calculations and filtering is allocated_capacity_gb.
.. note::
If max_over_subscription_ratio is not reported, the scheduler will use the
value defined on the [DEFAULT] section. This falls back to the default
value (20.0) if not set by the user.
[1] https://specs.openstack.org/openstack/cinder-specs/specs/queens/provisioning-improvements.html