Merge "Enhanced KVM Storage QoS"
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specs/rocky/approved/enhanced-kvm-storage-qos.rst
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specs/rocky/approved/enhanced-kvm-storage-qos.rst
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This work is licensed under a Creative Commons Attribution 3.0 Unported
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License.
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http://creativecommons.org/licenses/by/3.0/legalcode
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==========================================
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Enhanced KVM Storage QoS
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==========================================
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https://blueprints.launchpad.net/nova/+spec/enhanced-kvm-storage-qos
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QEMU 1.7 [1]_ and Libvirt 1.2.11 [2]_ [3]_ provides options to specify
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maximum burst IOPS and maximum burst bandwidth per disk.
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Additionally disk IO size can be specified as part of this version of QEMU.
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This blueprint proposes to add support for these additonal settings to
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QoS specs for connected volumes.
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Problem description
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===================
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At the moment, the Nova libvirt driver does not support setting storage IOPS
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limits. For this reason, some instances might exhaust storage resources,
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impacting other tenants.
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Use Cases
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----------
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* Associate burst IOPs and bandwidth front-end QoS specs for volumes
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exported through Cinder, which will be handled on the hypervisor side.
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This is in addition to the existing IOPs and bandwidth caps.
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* Set block IO size for IOPs to volumes exported through Cinder.
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* Set IOPs and bandwidth burst limits and block IO sizes for instance
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attached disks by using Cinder extra specs
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Proposed change
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===============
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Cinder attached volumes can have additional QoS specs assigned.
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Front-end QoS specs should be applied by Nova when the volume is attached.
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These are applied per volume.
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This blueprint proposes additional per volume QoS specs that will be
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specified using Cinder volume extra specs. The libvirt driver will apply
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those IOPS and bandwidth caps to the instance disks on a per volume basis.
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Additionally, this blueprint proposes adding the block IO size control using
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cinder volume extra specs to cinder attached volumes on a per volume basis.
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Front-end volume specs will be supported only in case of volumes exported
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through Cinder. No QoS specs are provided for local drives provided directly by
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Nova.
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Use case examples:
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* Admin sets front-end QoS specs on a specific volume type
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cinder qos-create my-qos consumer=front-end \
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total_bytes_sec_max=300000000 \
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cinder qos-associate my-qos <volume_type_id>
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cinder create <size> --volume-type <volume_type_id>
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# Those QoS specs are applied when the volume is
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# attached to a KVM instance
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nova volume-attach <instance_id> <volume_id>
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Available additional QoS specs, where each will add an extra
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line into the libvirt XML definition, specifically in the <iotune>
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section for each device, are:
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* read_bytes_sec_max
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add <read_bytes_sec_max>value</read_bytes_sec_max>
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* write_bytes_sec_max
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add <write_bytes_sec_max>value</write_bytes_sec_max>
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* total_bytes_sec_max - includes read/writes
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add <total_bytes_sec_max>value</total_bytes_sec_max>
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* read_iops_sec_max
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add <read_iops_sec_max>value</read_iops_sec_max>
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* write_iops_sec_max
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add <write_iops_sec_max>value</write_iops_sec_max>
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* total_iops_sec_max - includes read/writes
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add <total_iops_sec_max>value</total_iops_sec_max>
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* size_iops_sec
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add <size_iops_sec>value</size_iops_sec>
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Alternatives
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------------
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None
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Data model impact
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-----------------
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None
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REST API impact
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---------------
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None
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Security impact
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---------------
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None
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Notifications impact
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--------------------
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None
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Other end user impact
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---------------------
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As Nova supports N-1 version computes, if these new qoS specs are applied to a
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compute node running Queens, these new specs will be ignored. No error message
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will be provided from the Queens node.
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Existing Cinder QoS specs are documented in the Cinder Administration
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documentation set. [8]_
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Performance Impact
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------------------
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Allowing burst IOPs and bandwidth for certain volumes will allow some
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applications to better perform when required.
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Other deployer impact
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---------------------
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None
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Developer impact
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----------------
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None
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Upgrade impact
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--------------
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None
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Implementation
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==============
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Assignee(s)
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-----------
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Primary assignee:
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simon-dodsley
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Work Items
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----------
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* Add burst and IO size QoS specs support in the libvirt volume driver by
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extending the `nova/virt/libvirt/volumes/` block volume drivers to pass
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the new properties of a volume to `LibvirtConfigGuestDisk` via the
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`qos_specs' in the `connection_info` dict.
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* Extend the `LibvirtConfigGuestDisk` class to add the disk burst limits
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of a disk device [2]_
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Dependencies
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============
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* QEMU 1.7 [1]_
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* Libvirt 1.2.11 [2]_ [3]_
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QEMU included in Ubuntu 16.04 [4]_ [5]_ and libvirt at a higher version
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in Ubuntu 16.04 [4]_ [5]_. Also already included in Fedora 24 [6]_ [7]_
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Testing
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=======
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* Unit tests
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* Existing tests will ensure that the quest XML is formatted correctly
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assuming the required versions of libvirt and QEMU are present.
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Documentation Impact
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====================
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The additional QoS features are described in the libvirt driver
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documentation [1]_.
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Will update the Cinder Administrators Guide to add these new front-end
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QoS storage parameters.
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References
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==========
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.. [1] https://libvirt.org/formatdomain.html
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.. [2] https://libvirt.org/news-2014.html
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.. [3] https://www.redhat.com/archives/libvir-list/2014-August/msg01354.html
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.. [4] https://launchpad.net/ubuntu/+source/libvirt
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.. [5] https://launchpad.net/ubuntu/+source/qemu
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.. [6] https://apps.fedoraproject.org/packages/qemu
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.. [7] https://apps.fedoraproject.org/packages/libvirt
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.. [8] https://docs.openstack.org/cinder/latest/admin/blockstorage-capacity-based-qos.html
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History
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=======
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.. list-table:: Revisions
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:header-rows: 1
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* - Release Name
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- Description
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* - Rocky
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- Introduced
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