cinder/releasenotes/notes/bp-provisioning-improvements-bb7e28896e2a2539.yaml
Erlon R. Cruz f98c9da944 Overprovisioning Improvements
This is part of the effort to improve Cinder's Thin provisioning
support. As some operators have been facing problems to determinte
what is the best value for the max_over_subscription_ratio, we
add in this patch a mechanism to automatically calculate this value.

The formula used for calculation is:
max_over_subscription_ratio = 20 if provisioned_capacity_gb == 0 else:
max_over_subscription_ratio = 1 + (provisioned_capacity_gb/(
                             total_capacity_gb - free_capacity_gb + 1))

Using this formula, the scheduler will allow the creation of a much
bigger number of volumes at the begginning of the pool's life, and
start to restrict the creation as the free space approaces to 0 or
the reserved limit.

Drivers now can set max_over_subscription_ratio = 'auto' and take
benefit of the change. Drivers that somehow use the
max_over_subscription_ratio inside the driver to do any kind of
calculations are incompatible with this new feature and should
get fixed in order to be able to use the feature.

Implements: bp provisioning-improvements
Change-Id: If30bb6276f58532c0f78ac268544a8804008770e
2018-01-25 07:37:17 -02:00

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YAML

---
features:
- Cinder now supports the use of 'max_over_subscription_ratio = auto' which
automatically calculates the value for max_over_subscription_ratio in the
scheduler.