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Glossary

Instance/vm - Virtual machine running on a hypervisor. The terms may be used interchangeably.

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• For live migrating a volume from one storage pool to another, only the shared storage pools within the cluster should be listed.
• If storage tags were used in disk offerings, findStoragePoolsForMigration api should return the storage pools with matching tags as suitable. Other shared storage pools in the cluster should be marked unsuitable.
• Instance with one volume (only Root volume). Migrate volume of an instance from one shared storage pool to another within the cluster. At the end of the operation the volume should be on the destination pool and path updated in the db.
• Instance with multiple volumes (Root and Data volumes). Migrate one volume from one shared storage pool to another. At the end of the operation the volume should be on the destination pool and path updated in the db.
• Live migrating a virtual machine with its volumes, findHostsForMigration should return the list of hosts within the cluster and across cluster to which the vm can be migrated with volumes. The 'requiresStorageMotion' attribute should be set to true in the response.
• If host tags were used in service offering, findHostsForMigration api should return the hosts with matching tags as suitable. Other hosts should be marked as unsuitable.
• Migrate a vm from one host to another (migrateVirtualMachineWithVolume api) that do not have access to the same shared storage. Do not give a volume to pool mapping; that is, do not specify in the api which volume should be placed on which pool. The vm should be successfully live migrated with its volumes. The volumes created with shared disk offering should be placed on a shared storage pool and volumes with local disk offering placed on local storage pool.
• Validate that when a volume to pool mapping is given in migrateVirtualMachineWithVolume api, the volumes of a vm are placed on the given pool id.

Negative

• While migrating a virtual machine with a volume, gave an invalid volume to pool mapping; that is give a mapping for migrating a volume from shared to local or vice-verse. The operation should fail.
• Try live migrating a volume of a vm on a local storage. It should not be allowed.
• Live volume migration or live virtual machine migration with volume is a time consuming operation. When migration is going on, take the destination storage pool offline. Migration should fail and vm and its volume should be retained on the source host and storage pool respectively.

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This feature is implemented for Windows Server 2012 R2 and Hyper-V 2012 R2 (Core).

Use cases

• Live migrate volumes of a virtual machine from one storage pool to another. It could be because
  • The storage pool has to be brought down for maintenance.
  • Move the volumes to a storage pool which gives better performance/IOs etc.
• Live migrating a virtual machine with its volume on local storage to another host within or across cluster. The administrator doesn't want to bring down the services running on that virtual machine and the host has to be brought down for maintenance.
• Live migrating a virtual machine with its volume on shared storage to another host in a different cluster.
  • The administrator doesn't want to bring down the services running on that virtual machine and the host on which the instance is running has to be brought down for maintenance. Additionally, the cluster is running low on available capacity.
  • Live migrating a virtual machine with its volume to other hosts in different cluster to better distribute the load across hosts/clusters.

Architecture and Design description

Please refer to storage motion in cloudstack for details on how storage motion is implemented. The details on what is required for enabling it for Hyper-V are given below.

Migrating volume

• Volume service gets a request for migrating a volume to another storage pool.
• It dispatches a call (copyAsync) to the data motion service for migrating the volume.
• Data motion service checks which data motion strategy can handle migration of a volume to another pool.
• Data motion strategy (AncientDataMotionStrategy) issues a request (MigrateVolumeCommand) to the hypervisor resource (HypervDirectConnectedResource) to migrate the volume to a given storage pool.
• HypervDirectConnectedResource serializes the request and forwards the command to the Hyper-V agent running on the host for migrating the volume.
• The Hyper-V agent handles the MigrateVolumeCommand command. The command holds the information on
  • Which volume has to be live migrated.
  • The vm to which the volume is attached.
  • The destination pool for the volume.
• The agent lists all the volumes of the vm and identifies which volume needs to be migrated. It sets the updated path; from pool details; for the volume and issues a wmi request for migrating the volume.
• On success or failure of the operation, a response is send to the management server.
• On receiving the answer from the agent; the data motion strategy checks for success or failure of the operation.
  • On success the volume path is updated and volume moved out of migrating state.
  • On failure, the volume is moved out of migrating state and the failure logged and reported.

Migrating virtual machine with volume

• Virtual machine manager puts the vm to be migrated in 'Migrating' state and calls the volume service passing a volume to data store map. The map tells which volume of the vm needs to be migrated to which storage pool.
• Volume service puts the volumes to be migrated in 'Migrating' state and calls the data motion service.
• Data motion service checks which data motion strategy can handle migration of a vm and its volume. 'HypervStorageMotionStrategy' (a new strategy that is implemented for the hypervisor) returns true that it can handle the migration request for the hypervisor and request is forwarded to it.
• HypervStorageMotionStrategy issues a request (MigrateWithStorageCommand) to the hypervisor resource (source host) to migrate the vm with its volumes. The resource forwards it to the Hyper-V agent.
• The Hyper-V agent handles the MigrateWithStorageCommand. The command holds the following information
  • The vm to be migrated.
  • The destination host for the vm.
  • Volume to pool mapping; that is; which volume of the vm needs to be placed on which destination pool.
• The agent sets the new volume path for each volume of a vm and issues a wmi request for migrating the vm with its volumes to the destination host.
• On success or failure of the operation, a response is send to the management server.
• On receiving the answer from the agent; the storage motion strategy checks for success or failure of the operation.
  • On success the volume path is updated and volume and vm moved out of migrating state.
  • On failure, the volume and vm is moved out of migrating state and the failure logged and reported.

Database modifications

In the hypervisor_capabilities table, the entry for Hyper-V 2012 R2 is updated to allow storage migration. In column, storage_migration_supported, the value is set to 1 to allow storage motion for Hyper-V. 

Web Services APIs

No new apis are added for this feature. Existing apis; explained in Storage motion in cloudstack; will enable storage motion for Hyper-V too. List of apis used for storage motion

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No new UI screens are introduced by this feature. Also, no changes need to be made in UI for adding support for storage motion in Hyper-V. The UI workflow looks as follows.

Migrating

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volume

• From the Storage option in admin UI, select the volume that is attached to a running vm and has to be live migrated.
• Select the migrate option. 'findStoragePoolsForMigration' api is invoked by the UI. This will give a list of shared pools available to which the volume can be migrated.
• Selecting one of the storage pools and selecting ok will trigger issue the 'migrateVolume' api request to migrate the volume.

Migrate virtual machine with volume

• From the Instances option in the admin UI, select the instance that needs to be migrated (with its volumes).
• Select the migrate option. 'findHostsForMigration' api is invoked by the UI. This will give a list of hosts to which the vm can be migrated.
• If migrating to a host requires storage motion too, 'requiresStorageMotion' flag is set to true in the response and the UI shows it as "Storage migration required".
• Selecting a host; to which storage mition is required; will trigger issue the 'migrateVirtualMachineWithVolume' api request.

IP Clearance

No IP dependencies are introduced by this feature.

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