VMware: support for vSAN datastores
Proposal to add support for vSAN storage to the vmware nova driver. Previously-approved: juno Change-Id: Ib221e55659f6113bc4f8c86506a790330b5722af
This commit is contained in:
Radoslav Gerganov
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specs/kilo/approved/vmware-vsan-support.rst
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specs/kilo/approved/vmware-vsan-support.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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VMware: Support for vSAN Datastores
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===================================
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https://blueprints.launchpad.net/nova/+spec/vmware-vsan-support
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Currently the vmwareapi compute driver only supports deploying instances to NFS
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and VMFS datastores. This blueprint proposes to add support for using vSAN
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storage as well.
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Explanation of terminology used:
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The term "datastore" as referred to in the spec and the driver refers to
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the vSphere concept a logical storage container, a place where VM data (among
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other things) is kept. The purpose of this abstraction is to provide a uniform
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way for vSphere clients to access said VM data regardless of what hardware, I/O
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protocols or transport protocols are used by the underlying storage.
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All vSphere datastores until recently has been broadly divided into two types,
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VMFS and NFS. The vmwareapi driver has been supporting the use of both since
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its inception, without having to distinguish between either, largely because of
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this datastore abstraction.
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vSAN storage is a third type of datastore introduced in vSphere. It is
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a software-defined distributed storage that aggregates disks (magnetic for
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capacity, SSD for cache/performance) attached to a group of hosts into a
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single storage pool. That pool is once again exposed as a single datastore.
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Problem description
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===================
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Currently datastores with type "vsan" is ignored by compute driver entirely.
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One obstacle to using this type of datastore is that virtual disk data files
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(the "-flat.vmdk" files) are not directly addressable as datastore paths. Since
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both the spawn and snapshot workflow in the vmware driver addresses the data
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files in some way, they will have to be changed to support vSAN datastores.
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Use Cases
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----------
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The End User will be able to use vSAN datastores and deploy streamOptimized
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images.
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Project Priority
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-----------------
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None
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Proposed change
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===============
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The change is divided into two areas:
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* Recognize and use datastores of a new type ("vsan").
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* Update existing code involved in exporting and importing Glance images to
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use alternate vSphere APIs that does not address disk data files directly.
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The second area of change is mainly provided by the image-transfer
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functionality in the oslo.vmware library [*]_. The proposal is to update the
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code to use said library.
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However, the only disk format that these alternate APIs support is the
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'streamOptimized' format. (The streamOptimized format is a sparse, compressed,
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and stream-friendly version of the VMDK disk that is well suited for
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import/export use cases, such as the glance<->hypervisor exchanges described
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above). This implies that only streamOptimized disk images are deployable on
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vSAN. The driver will be modified to recognize Glance vmdk images tagged
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with the property vmware_disktype='streamOptimized' as disks of such format,
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and only use the alternate APIs when handling disks of this format.
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.. [*] To import a disk image to a vSAN datastore, oslo.vmware uses the
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ImportVApp vSphere API is used to import the image as a shadow virtual
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machine (a VM container to hold a reference to the base disk disk, and is
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not meant to be powered on). Likewise, to export the disk image, the library
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uses the ExportVM vSphere API. These APIs do not reference the virtual disk
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data file paths directly and are hence compatible with vSAN storage.
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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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None
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Performance Impact
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------------------
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None
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Other deployer impact
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---------------------
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There is a new configuration option under the [vmware] section,
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"image_transfer_timeout_secs", which configures how long an image transfer can
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proceed before timing out.
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In order to deploy existing VMDK images to vSAN, these images will have to be
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converted to streamOptimized and reimported to glance.
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Developer impact
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----------------
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Minimal. The changes related to blueprint are mostly isolated in the areas of
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handling a new vmdk format type and add recognition and use of an additional
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datastore type called "vsan".
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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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rgerganov
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Work Items
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----------
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The work is broadly decomposed into:
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* use oslo.vmware image_transfer module to handle download of images
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* use oslo.vmware image_transfer module to handle upload of image snapshot
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* update driver to allow the use of datastores of type vSAN.
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* update driver to recognized a new vmdk format (streamOptimized)
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Dependencies
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============
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None
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Testing
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=======
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Since Tempest in general does not support driver-specific tests, the proposal
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is to update the MineSweeper CI
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(https://wiki.openstack.org/wiki/NovaVMware/Minesweeper), to provide
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vCenter with vSAN storage and additional tests to verify existing Tempest
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tests passes when invoked against compute nodes using it.
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Documentation Impact
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====================
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New information in the vmware driver section of the Nova documentation will
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have to be added to document:
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* How to configure a compute node for vSAN use.
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* The virtual disk format requirement ("streamOptimized" only) when using vSAN
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storage.
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* The new "image_transfer_timeout_secs" configuration option.
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* How to obtain a streamOptimized disk from a virtual machine or vmdk disk in a
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non-streamOptimized format.
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References
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==========
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* https://github.com/openstack/oslo.vmware
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* https://wiki.openstack.org/wiki/NovaVMware/Minesweeper
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