Today I’ve found an question in the VMware Enterprise Desktop online community forums where a member asked if someone could explain the difference between the terms Reset, Refresh, Recompose and Rebalance in context of VMware View. Some of you are familiar with that but I think it’s worth to explain.
A reset can be done by either the administrator or by the user if he has the permission to do that. This permission can be given to the user during the pool or desktop configuration. This is interesting for the user as a self service if something goes wrong with his VM. The option "Reset" in the View Administrator shows the following message when clicked.
This does explain what happens when reset the desktop! It just resets the Virtual Machine without shutting down the operating system properly like it does when clicking the reset option in the vCenter. The user session will be disconnected and all unsaved work will be lost.
The term Refresh and Recompose came with the first version of the View Composer into the game. Those to words describe two highly important functions of the Linked Clone technology uses in VMware View. If you are not familiar with the View Composer, here is a quick introduction. The VMware View Composer does use the linked clone technology what means that multiple virtual machine disks are based on one master image where they read from. They also have their own disk called delta disk where they write changes to. To create a linked clone pool you’ve to use a virtual machine, not a virtual machine template as you do with the traditional pool. This virtual machine has to be added to the Active Directory domain and be shut down before you create a snapshot of it. Linked Clone pools are based on snapshots but it only works if the virtual machine was shut down when creating it. During the desktop pool wizard setup you will be asked for the golden master image which is the virtual machine you’ve already prepared. In the next step the wizard will give you an overview of all snapshots of the virtual machine and you’ve to select one of them. When you’ve finished the pool wizard the View Manager / View Composer will start to create the pool. First a full clone will be provisioned from the snapshot you’ve selected to each LUN configured in one of the wizard steps. This is called the Replica image. After that it creates a thin one named source which is the first linked clone. This one is copied into each of the pool’s VM’s. For now it is very thin but it will growth when the virtual machine is running due to changes in the operating system and of course paging. All virtual machines will be personalized with hostname and more details through the Quickprep process when they start up. With the Recompose and Refresh functions you can now shrink the current VM again or re-create it with another Windows service pack maybe or just installed with some new security fixes installed.
The Recompose action is done by the Administrator within the View Administrator interface. With this function the Administrator can change the snapshot within the parent VM or he can change to another parent VM. In both cases a new Replica image will be provisioned to all LUN’s configured with the pool.
During the refresh the snapshot or parent VM isn’t changed. This action does only reset the delta disk to it’s initial state, to the source. This is be done to reduce the amount of storage used by the VM.
Both options are only available in a persistent automated linked clone pool and not in a non-persistent pool. To refresh a non-persistent pool all VM’s need to be re-created. A good option here is to delete the VM’s after first use and personalize them with roaming profiles and scripting or with a profile management solution like AppSense Environment Manager or RTO.
In a persistent linked clone pool all application data should be redirected to the user data disk which also stores the user profile because the data on drive C:\ will be lost when refreshing or recomposing the disk.
During this action all virtual machines will be rebalanced between the LUN’s to use the space efficiently.
More information about that is available in the VMware View Administrator Guide. For version 3.1 starting on side 119.