openstack/cinder-specs
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48f54bab22
cinder-specs/specs/juno/support-volume-num-weighter.rst
zhangbailin 456b86528d Modify spelling mistakes 
When I read this specs file, I found a lot of spelling mistakes,
and I made a change here to give you a good code reading experience.

In specs, modify "acording" to "according" and  "priviledges" to
"privileges" and "Additionaly" to "Additionally" and so on. you can
get them from the "File Path" in the web.

Change-Id: I95228e1a57c7aa588c78d4a3af46b18daadac01d
2017-08-14 17:55:30 -07:00

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Support Volume Num Weighter

Include the URL of your launchpad blueprint:

https://blueprints.launchpad.net/cinder/+spec/support-volume-num-weighter

Provide a mean to help improve volume-backends' IO balance and volumes' IO performance.

Problem description

Currently cinder support choosing volume backend according to free_capacity and allocated_capacity. Volume Num Weighter is that scheduler could choose volume backend based on volume number in volume backend, which could provide another mean to help improve volume-backends' IO balance and volumes' IO performance.

Explain the benefit from volume number weighter by this use case.

Assume we have volume-backend-A with 300G and volume-backend-B with 100G. Volume-backend-A's IO capabilities is the same volume-backend-B IO capabilities. Each volume's IO usage are almost the same. Use CapacityWeigher as weighter class.

Concrete Use Case: If we create six 10G volumes, these volumes would placed in volume-backend A. All the six volume IO stream has been push on volume-backend-A, which would cause volume-backend-A does much IO scheduling work. At the same time, volume-backend-B has no volume and its IO capabilites has been wasted.

If we have volume number weighter, scheduler could do proper initial placement for these volumes----three on volume-backend A, three on volume-backend-B. So that we can make full use of all volume-backends' IO capabilities to help improve volume-backends' IO balance and volumes' IO performance.

Use Cases

Proposed change

Implement a volume number weighter:VolumeNumberWeighter.
  1. _weigh_object function return volume-backend's non-deleted volume number by using db api volume_get_all_by_host.
  2. Add a new config item volume_num_weight_multiplier and its default value is -1, which means to spread volume among volume backend according to volume-backend's non-deleted volume number.

Since VolumeNumberWeighter is mutually exclusive with CapacityWeigher/AllocatedCapacityWeigher and cinder's scheduler_default_weighers is CapacityWeigher, we could set scheduler_default_weighers=VolumeNumberWeighter in /etc/cinder/cinder.conf and restart cinder-scheduler to make VolumeNumberWeighter effect.

VolumeNumberWeighter, whichi provides a mean to help improve volume-backends' IO balance and volumes' IO performance, could not replace CapacityWeigher/AllocatedCapacityWeigher, because CapacityWeigher/AllocatedCapacityWeigher could be used to provide balance of volume-backends' free storage space when user focus more on free space balance between volume-bakends.

Alternatives

None.

Data model impact

None

REST API impact

None

Security impact

None

Notifications impact

None

Other end user impact

None

Performance Impact

None

Other deployer impact

None

Developer impact

None

Implementation

Assignee(s)

Primary assignee:

ling-yun

Work Items

  • Implement Volume Number Weighter
  • Add weighter option of Volume Number Weighter to OPENSTACK CONFIGURATION REFERENCE

Dependencies

None

Testing

Set up volume-backend-A with 300G and volume-backend-B with 100G. Create six 10G volumes, the expected result is 3 volumes in volume-backend A and 3 volumes in volume-backend B.

Documentation Impact

Add weighter option of Volume Number Weighter to OPENSTACK CONFIGURATION REFERENCE.

References

None