Here's some advice from Charlie Rizor, a support engineer specializing in Enterprise Desktop virtualization.
The Enterprise Desktop team at VMware support receives many support requests from customers that have performed an upgrade of their vSphere or View environments, and are now unable to provision desktops or connect to their environment. The majority of these cases could be avoided with a little understanding and planning prior to pulling the trigger on an upgrade.
Here is a list of the top 5 actions you can take during the planning phase to improve your upgrade experience.
1. Read the Documentation before upgrading.
It may not be necessary to read every document before installing a View test environment, but before upgrading a production environment, you should be familiar with the release notes and the upgrade guide. It cannot be overstated how many times reading just these documents would save hours of work in troubleshooting and rebuilding a View infrastructure. View 5.1 in particular has a lot of changes to the way security features are handled, and blindly upgrading without understanding these changes will almost certainly result in a broken View environment. Refer to the View Documentation site, https://www.vmware.com/support/pubs/view_pubs.html
2. Before upgrading to the latest version of vSphere, verify that View Manager and Composer are compatible.
Due to offset release cycles, View Composer is not generally compatible with the latest vCenter Server the day it releases. View relies on the APIs present in vSphere to perform provisioning operations and is not designed to work with future vCenter Server releases. If your organization has a separate administrator for vSphere, be sure they understand that View must be considered prior to upgrading the virtual infrastructure. For example, vSphere 5.0 requires View to be at least version 5.0. See vSphere 5.x does not support View Manager 4.x (2006216).
3. Don’t change the name or IP address of the vCenter Server during an upgrade.
When creating a pool in View, you designate the vCenter Server, Datacenter, and Cluster under which that pool is to be deployed. Changing the identity of any of these will break provisioning. The only supported way to change the identity of the vCenter Server in View is to delete all the desktops and pools, remove the vCenter Server from the View Configuration and add the vCenter Server with the new identity. For information on verifying continuity between vSphere and View components, see Editing an existing pool in the VMware View web admin interface fails with the error: One of required objects is not found in the VirtualCenter server <IP address> (1015100).
4. During the Upgrade process, some operations are not available.
There are many pieces to a View infrastructure, and once the upgrade process is started, some operations are not available until all the components are upgraded. Check the View Component Compatibility Matrix in the Upgrade Guide for specifics, but in general you will be able to continue connecting to current desktops during the upgrade, but provisioning new desktops is not possible until the Agent, Connection Server and Composer versions are fully compatible.
5. Backup your View environment and disable provisioning during the upgrade to give you a restore point.
View 5.1 doesn’t leave you the option to downgrade after installing, but if your servers are virtual machines in your vSphere environment, you can take a snapshot of them prior to running the installer to give yourself a fallback if the upgrade has to be aborted. This will only work if the information in the databases is consistent with the state of the View environment, so be sure to disable provisioning before taking this snapshot and keep it disabled until the upgrade is complete, then delete the snapshots once the upgrade is verified.
The View Upgrade Guide also contains a section entitled Preparing for a VMware View Upgrade which will walk you through the steps of setting up backup and restore points prior to installing the latest software. For View 5.1, there is an html version located here, but see the VMware View Documentation page for your version.
By keeping these simple points in mind, you give yourself the best chance of having a smooth upgrade with minimal downtime.