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Linked-clone lifecycle in VMware View Manager 4.5 and later releases (1021506)

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View Manager 4.5 introduces new View Composer features that affect the way linked clones are managed throughout their lifecycle. Linked clones have been a View component since View Manager 3.0.

This article describes how linked clones are provisioned, customized, refreshed, recomposed, and rebalanced in View Manager 4.5 and later releases. This article focuses on internal operations, not user interfaces or procedures.

Solution

Provisioning and Customization

The first phase in the linked-clone lifecycle is provisioning. View Manager initiates the creation of a linked clone by making a call to the View Composer service to create the linked clone. The View Composer service makes a call to vCenter Server, which sends a request to an ESX server to create the linked clone.

The second phase in the lifecycle is customization. Each linked clone must be given a unique identity in the domain before a user can log in to the virtual machine. Before View 4.5, VMware QuickPrep was the only available customization method. View 4.5 introduced support for the Microsoft Sysprep customization method. An administrator can use either QuickPrep or Sysprep customization when creating a linked-clone pool.

Provisioning

These steps describe the operations by which linked clones are created and provisioned:
  1. View Manager creates the linked-clone entry in View LDAP and puts the virtual machine into the Provisioning state.
  2. View Manager calls View Composer to create the linked clone
  3. The View Composer Server creates the machine account entry in Active Directory for the new clone and creates a random binary password for the newly created computer account.
  4. If a replica for the base image and snapshot does not yet exist in the target datastore for the linked clone, View Composer creates the replica in the datastore. If a separate datastore is configured to store all replicas, the replica is created in the replica datastore. (In View 4.5 and later, replicas can be stored in a separate datastore.)
  5. View Composer creates the linked clone using the vCenter Server API.
  6. View Composer creates an internal disk on the linked clone. This small disk contains configuration data for QuickPrep or Sysprep. The disk also stores machine password changes that Windows performs every 30 days, according to the policy setting. This disk data ensures that domain connectivity is maintained when a checkpointed desktop is refreshed.
Customization

These steps describe the operations by which linked clones are created and customized:
  1. View Manager puts the virtual machine into the Customizing state.
  2. If the pool is configured to use Sysprep, View Manager calls the vCenter Server API customizeVM_Task to customize the virtual machine with the customization spec. Note that domain / administrator information in the customization spec is not used. The virtual machine is joined to the domain using the guest customization information entered through the View Administrator UI. For more information, see Sysprep workflow during linked clone creation in VMware View 4.5 and later (1029894)
  3. View Manager powers on the linked clone.
  4. When the virtual machine powers on, in the guest operating system on the linked clone, the View Composer Agent detects that it is starting for the first time and calls NetJoinDomain with the machine password cached on the internal disk. The machine is now joined to the domain. This operation takes place for both QuickPrep and Sysprep.
  5. If Sysprep is being used, Sysprep runs in the guest operating system on the linked clone.
  6. The View Composer Agent waits for Sysprep to finish before notifying View Agent that customization is complete.
  7. View Agent waits for the View Composer Agent to say that customization is complete. When customization is complete, View Agent sends a message to View Manager.
  8. View Manager powers off the clone and takes a snapshot of the customized, powered off clone. The snapshot is called “vdm-initial-checkpoint”.
  9. When the linked clone is created and customized, and a snapshot has been taken, View Manager puts the linked clone into the Provisioned state. If the virtual machine is powered on, it changes to the Available state.

Ongoing Operation

While a linked clone is powered on and the View Composer Agent is running, the View Composer Agent tracks any changes made to the machine account password.

In many Active Directory environments, the machine account password is changed periodically. If the View Composer Agent detects a password change, it updates the machine account password on the internal disk that was created with the linked clone. During a refresh operation, when the linked clone is reverted to the snapshot taken after customization, the agent can reset the machine account password to the latest one.

Refresh

In View 4.5 and later, a refresh triggers a revert operation to the snapshot that was taken after customization was completed. This approach allows View to preserve the customization performed by Sysprep. Before View 4.5, a refresh operation essentially deleted the current operating system disk for the linked clone and created a new operating system disk.

These steps occur during a refresh:

  1. View Manager puts the virtual machine into the Maintenance state.
  2. View Manager reverts the virtual machine to the post-customization snapshot vdm-initial-checkpoint. Only the operating system disk is checkpointed. All other disks are created as independent disks and are not part of the snapshot.
  3. View Manager changes the virtual machine state to Provisioned. If the virtual machine is powered on, it moves into the Available state.
  4. When the guest operating system starts up again, the View Composer Agent determines if it needs to update the machine account password. If the machine account password saved in the internal disk is newer than the one in the registry, the agent updates the machine account password with the one stored in the internal disk to maintain domain connectivity.

Recompose

A recompose operation lets the administrator preserve the View Composer persistent disk and all user data inside this disk while changing the operating system disk to a new base image and snapshot. With recompose, an administrator can easily distribute operating system patches and new software to users. Recomposing between major operating system versions are not supported (XP >Vista, XP >Windows7, Vista >Windows7).

Because a new operating system  disk is created during a recompose, the clone is also customized again during the recompose operation. When the customization is completed, View Manager takes a new snapshot.

These steps occur during a recompose operation:

  1. View Manager puts the linked clone into the Maintenance state.
  2. View Manager calls the View Composer resync API for the linked clones being recomposed, directing View Composer to use the new base image and snapshot.
  3. If a replica for the base image and snapshot does not yet exist in the target datastore for the linked clone,View Composer creates the replica in the datastore. If a separate datastore is configured to store all replicas, a replica is created in the replica datastore.
  4. View Composer deletes the current operating system disk for the linked clone and creates a new operating system disk, linked to the new replica.
  5. The rest of the recompose cycle is identical to the customization phase of the provisioning and customization cycle.

Rebalance

The rebalance operation redistributes linked clones among available datastores to take advantage of free storage space. In View 4.5 and later, there is no other supported way to move linked clones from one datastore to another.

A rebalance operation might not redistribute any linked clones. If all the datastores have approximately the same amount of free space, moving linked clones from one datastore to another would not free up more space. A rebalance only moves linked clones if one of the datastores configured for the pool has substantially less free space than the others.

These steps occur during a rebalance operation:

  1. View Manager puts the linked clone into the Maintenance state.
  2. View Manager determines which virtual machines to move based on the free space in each datastore. For a discussion on how storage is managed and how View decides which datastores to use, see the Storage Overcommit for Linked-Clone Desktops section of the VMware View Administrator's Guide.
  3. View Manager detaches the operating system and persistent disks from the virtual machine.
  4. View Manager moves the detached persistent disks to the new datastore.
  5. View Manager moves the virtual machine itself to the new datastore using the relocateVM_Task API.
  6. View Manager re-attaches the disks to the linked clone.
  7. View Manager calls the View Composer resync API for the linked clones.
  8. If a replica for the base image and snapshot does not yet exist in the target datastore for the linked clone, View Composer creates the replica in the datastore. If a separate datastore is configured to store all replicas, a replica is created in the replica datastore.
  9. View Composer deletes the current operating system disk for the linked clone and creates a new operating system disk, linked to the appropriate replica.
  10. The rest of the recompose cycle is identical to the customization phase of the provisioning and customization cycle.

Additional Information

For translated versions of this article, see:

Update History

01/30/2012 - Updated to include View Manager 5.0 02/13/2012 - Added link to Japanese translation 01/07/2012 - Added View Manager 5.1.x to Product Versions 09/20/2013 - Added View 5.2 to product versions 11/28/2013 - Added link to article 1029894

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ja,2013650

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