Is vSphere 4 and vSphere 5 compatible or upgrade?

[grumpy1965]

I have two dual processor servers running vSphere 4. As part of the a DR plan we will be replicating the VM's to another location. We are purchasing a new license for the target server. Naturally the new server will be running vSphere 5. In the event we fail over to the DR site and then roll back to the original site.  Am I right in assuming we'll experince compatibility issues when trying to move the machines back from v5 to v4?

Is there an upgrade path that upgrade the 4 processor licenses from v4 to v5 and include 4 new licenses for v5. What's the most economical method?

[Dave_Mishchenko]

A VM can be run on vSphere 5 and then again on 4.  You would have to keep the virtual machine version at 7 to accomplish this, but you could upgrade VMware Tools without negative impact.   A virtual machine with a virtual machine version of 8 can not be run on vSphere 4 (in such a case you would have to use something like VMware Converter to migrate the VM to a version that could run on vSphere 4).

What license edition do you have on the vSphere 4 host?  There are some acceleration kits that include vCenter and host licensing which might work for you.

[grumpy1965]

We have vSphere v4 standard on the 2 VMhosts with 2 processors each. The new host is a 4 processor machine.