Hyper-V Storage QoS


Hyper-V provides options to specify maximum IOPS per virtual disk image.

By leveraging this feature, this blueprint proposes to add support for setting QoS specs targeting instance local disks as well as volumes exported through SMB.

Problem description

At the moment, the Nova Hyper-V driver does not support setting storage IOPS limits. For this reason, some instances might exhaust storage resources, impacting other tenants.

Use Cases

  • Associate front-end QoS specs for volumes exported through SMB, which will be handled on the hypervisor side

  • Set IOPS caps for instance local disks by using flavor extra specs

Proposed change

Cinder volumes can have QoS specs assigned. Front-end QoS specs should be applied by Nova when the volume is attached. Those are applied per volume.

In addition, this blueprint proposes per instance QoS specs that will be specified using flavor extra specs. The Hyper-V driver will apply those IOPS caps to all the local instance disks equally.

For example, if a specific IOPS cap is specified in the flavor extra specs, this cap will be applied to the instance root, ephemeral and configdrive disk equally.

Front-end volume specs will be supported only in case of volumes exported through SMB.

Use case examples:

  • Admin sets front-end QoS specs on a specific volume type
    cinder qos-create my-qos consumer=front-end


    cinder qos-associate my-qos <volume_type_id>

    # SMB must be used as a volume backend, iSCSI support may be # added in the future cinder create <size> –volume-type <volume_type_id>

    # Those QoS specs are applied when the volume is # attached to a Hyper-V instance nova volume-attach <hyperv_instance_id> <volume_id>

  • Admin sets instance storage QoS specs on the flavor
    nova flavor-key <my_flavor> set


Available QoS specs:
  • total_bytes_sec - includes read/writes

  • total_iops_sec


Flavor QoS specs could be applied not only for instance local disks but attached volumes as well. In this case, if volume QoS specs are present, we may apply the lowest IOPS cap.

Also, the cap could be divided among the disks, but this may not be desired.

Data model impact


REST API impact


Security impact

Setting storage QoS specs will prevent instances from exhausting storage resources, which may impact other tenants.

Notifications impact


Other end user impact


Performance Impact

Preventing instances from exhausting storage resources can have a significant performance impact.

Other deployer impact


Developer impact




Primary assignee:

Lucian Petrut <lpetrut@cloudbasesolutions.com>

Work Items

  • Add front-end QoS specs support in the Hyper-V SMB volume driver

  • Add flavor storage QoS specs support




This feature will be tested by the Hyper-V CI. We’ll add tempest tests verifying that the IOPS cap is actually enforced.

Documentation Impact

The QoS features should be described in the Hyper-V driver documentation.


Hyper-V Storage QoS reference: https://technet.microsoft.com/en-us/library/dn282281.aspx