Managing Linked Clones

Introduction Managing Linked Clones

Version: Horizon View 5.1

Once a linked clone desktop pool has been created, you have a few additional options or controls to manage them back on the main management webpage – VMware uses the terms Refresh, Recompose and Rebalance to describe the three main tasks that may need to be carried out on your linked clones. VMware uses quite neutral-sounding terms for these tasks – the words “refresh”, “recompose” and “rebalance” sound quite reassuring and non-intrusive. Don’t be fooled by the soft-sounding words, these changes have a huge impact on users and can take some time to complete, depending on the number of virtual desktops in the pool.

Refresh – This option resets the delta disks back to the original state. If you are familiar with VMware Snapshots, the process is analogous to reverting the VM back to its original state when it was first created. Any modifications the user has made to the virtual desktop will be discarded. Remember, this option can also be triggered by the logoff event (using the Pool Settings page), so every time the user logs off, the delta disk is discarded and regenerated. A refresh can be quite an intrusive task because if affected users are currently logged in, they will receive a message forcing them to log out of their environment. The virtual desktops are all powered off and new delta virtual disks are created. When refreshing desktops or choosing to set the desktops to refresh on logout you will need to take into consideration the increase in IOPS during a refresh operation, if a larger pool is refreshing or if all your users logout at the same time the impact on the storage could be considerable.

Recompose – In this process, the linked clones are attached to a new replica. The net effect is that all the changes accrued in the delta disk are lost, and users get a brand new virtual desktop. The Recompose command can be used to roll out new software or a new service pack – effectively replacing the virtual desktop with a new build without having to re-create the virtual desktop pool and entitlements. A recompose is a very intrusive task – if affected users are currently logged in, they will receive a message forcing them to log out of their environment.

Rebalance – This option is there if you have selected different storage locations for your virtual desktops. It could be the case that you have more virtual desktops in one datastore than another. The Rebalance command attempts to redistribute the VMs evenly among the datastores. It’s essentially a storage management option.

Refresh Virtual Desktops in the Pool

It is possible to refresh every virtual desktop in the pool, or by selecting individual virtual desktops in the list, only selected desktops get refreshed. To test this and other features, we made a point of making changes to the user’s environment. So, in one case we made the desktop a bright pink and created a file that shouldn’t have been there! NICE!

Remember that these changes go to the user’s profile, and in the steps we outlined earlier we set a persistent disk. So, although changes in the operating system will be reset, the changes made to the profile disk will be kept. This means you can safely reset the operating system without losing the user’s settings or data held in user profile locations such as their Desktop or My Documents folders.


1. In the >Inventory

2. Select Pools and Select the Pool you wish to modify:

3. Select the desktop(s) you wish to refresh. The system will allow you to use shift+click to bulk select desktops, and ctrl+click to select disparate desktops. Notice in the screen grab below, we have selected a desktop that we know has a user connected. Next click the View Composer button and select Refresh


It is possible to refresh the entire desktop, from the Settings tab on the properties of the pool


4. This will bring up the Refresh page, which controls what will happen to users when the refresh occurs. We think this is fairly self-explanatory.


As you can see you set a time for the event, which allows you to defer the refresh until a more suitable and less intrusive time. You can force users to log off, which will send them a warning message (configurable under the global settings) and give them 5 minutes to save their work (also configurable). We think these are quite dangerous settings, given that users tend to leave themselves logged in whilst chatting around the water cooler. Alternatively, you can wait until users log off for the refresh event to take place. The dialog box looks like this:


Note: The outcome of this process should result in the use user getting a brand new copy of Windows without losing their settings – as these have been stored in the Persistent Disk. Alternatively, if you redirect the Windows profile to the network (aka the roaming profile) then the users settings should not be lost in this process.

Recompose a Linked Clone Virtual Desktop

There are a number of ways to recompose a linked clone. You can either attach a brand new parent, or snapshot the existing parent with new changes. Remember, a recompose is essentially a quick way of pushing out a new build of the corporate desktop. We would recompose with a new snapshot if we were making a major change such as rolling out a service pack or upgrading the web browser from one version to another. In our example below, we are going to install VLC media player on our Windows 7 desktops.

WARNING: DO NOT use this feature to roll out a new operating system, such as switching from a Windows XP virtual desktop to a Windows 7 virtual desktop. You are far better off creating a brand new pool and assigning and un-assigning the users accordingly. Additionally, if you re-parent the VMs with a new parent of the SAME operating system type, ensure that the VM Hardware versions match. Otherwise you can anticipate fun and games when you try and power on the VMs after the recompose:


1. Power on the Parent VM

Remember you can make changes to the Parent VM at any time. The linked clones get their data from the replica of the Parent VM

2. Log in and make your changes, in our case we downloaded and installed VLC Media Player

3. Once you have made your updates, release the IP address of the Parent VM with ipconfig /release

4. Power off the Parent VM, and create a new snapshot. In our case, we called it “Media Player Upgrade”

5. In the >Inventory

6. Select Pools and Select the Pool you wish to modify:


Note: As with the refresh option you are able to select individual desktop for a recompose as well.


7. The large change button allows you to completely alter the base image used for the linked clone. In our case however, we have only made a slight modification to the Parent VM. Remember, the Parent VM can have multiple snapshots used by multiple desktop pools. This means that you don’t have to maintain a separate Parent VM for each different type of desktop pool you have – just a different snapshot for each desktop pool you maintain – although many administrators prefer to do precisely that.


As with refreshing a desktop, you can schedule when this event will occur, View will then orchestrate the whole process of logging out users and will then proceed to power off each virtual desktop and delete it. Once all the desktops have been destroyed, View sets about creating a brand new set of virtual desktops from a new replica based on the new snapshot – in our case called Media Player Upgrade. During this process, you will see that the old replica files are unregistered and deleted.

This is clearly a very intrusive task to the end users, but saves time for administrators since you don’t have to create a new pool with new settings every time you need to make a change to the OS. However, as it effectively destroys the old pool and creates a new one, it’s important to note that a recompose is not a trivial event.

The screen grab below shows the recompose in mid-cycle – with a an additional replica has been generated, with the older replica yet to be destroyed.


Rebalance a Linked Clone Virtual Desktop

1. In the >Inventory

2. Select Pools and Select the Pool you wish to modify

3. Select the desktop(s) you wish to rebalance. The system will allow you to use shift+click to bulk select desktops, and ctrl+click to select disparate desktops. Notice in the screen grab below, we have selected a desktop that we know has a user connected. Next click the View Composer button and select Rebalance



Like with the other linked clone operations the rebalance feature allows you to schedule when the operation will be undertaken and also gives you the option of what to do if there are users currently logged into the desktops.


Once you complete this wizard the virtual desktops will be refreshed and rebalanced over the chosen datastores using a weighting system that is calculated as follows:

datastore_capacity x over_commit_factor – virtualusage

The over commit factor is determined depending on what the value of over commitment you selected when creating your pool. The values are as follows.

With None , Storage is not overcommitted.

With Conservative, the overcommit is 4 times the size of the datastore. This is the default level.

With Moderate, the overcommit is 7 times the size of the datastore.

With Aggressive, the overcommit is 15 times the size of the datastore.

Virtual usage is calculated by working out the maximum possible datastore usage by all desktops that have already been created.

For a better understanding of the rebalance operation we can highly recommend taking a look at fellow vExpert Simon Long’s blogpost


In this chapter we have covered some of the most important features of VMware view, the use of linked clones and the ability to refresh and recompose these desktops gives us an incredible amount of freedom and the ability to send updates across a whole organisation’s desktops in a very short period of time With the added ability to schedule these updates at the most convenient time for the business, it all adds to the ability of releasing the administrative burden from the IT / Desktop teams. Our next chapter will move on to explain what the storage vendors are doing to allow linked clone style features to happen natively within their products.



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