I wrote an article a couple of weeks ago about the incompatibility of VMware View 5.1 and vSphere 5.1, but mentioned a forthcoming patch based on an update to VMware knowledge base article 2035268 (https://kb.vmware.com/kb/2035268) that I saw through a RSS subscription to the article. Good news as of last night – that patch is now available for download, making vSphere 5.1 compatible with View 5.1. I am a bit surprised that the patch, ESXi510-201210401-BG, applies to ESXi 5.1 instead of View 5.1. I would expect that the older View 5.1 (released in May 2012) would need to be patched to work with the newer ESXi 5.1 (released in September 2012). The fix for ESXi 5.1 corrects an issue with the View Storage Accelerator’s use of the Content Based Read Cache (CBRC) functionality in ESXi. Without the patch, multiple CBRC disable requests issued from View to hostd might cause View to lose connectivity to an ESXi host.
While this compatibility does not mean that you’ll be able to start using the new View-targeted features in vSphere 5.1 such as the new Space Efficient Sparse Disk vmdk format or virtual shared graphics acceleration (including 3D graphics), it does allow VMware admins to begin upgrading their environments to take advantage of the other new features in vSphere 5.1 such as 32-host clusters for Linked Clones (up from 8 hosts), the improved vSphere Distributed Switch, vSphere Data Protection for full clone or manual desktop backups, and the new vSphere Web Client.
As with any upgrades, be sure to first check the VMware Product Compatibility Matrix at https://partnerweb.vmware.com/comp_guide2/sim/interop_matrix.php to make sure the components you are putting together are compatible and there are no known caveats.