Erlon R. Cruz e3cdd6b8c8 Updates overprovisioning dev-ref

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

2018-04-27 15:03:32 -03:00

1.7 KiB

Raw Blame History

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

thin_provisioning_support = True (or False)

Optional Fields

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.