I'm using a 2-node VSA Cluster. I recently upgraded vCenter and both ESX hosts to 5.5 U1. The upgrade went fine including VSA Manager 5.5.
The VSA Cluster version still remains on version 5.1.1 as well the VSA Cluster Service which I back then installed on a separate Linux machine (vCenter and the VSA Cluster service on linux box runs on a third smaller ESX server independant from VSA Cluster).
Did someone already made an upgrade of the VSA Cluster from 5.1 to 5.5? The steps seems very easy, I guess first I need to change the VSA Cluster password to the default (mentioned in release notes) then shutdown all VM's (no I/O on datastores) and then press the upgrade button. But I'm a little afraid of doing that.
The right procedure for VSA upgrade involves, upgrading the VSA appliance, check if everything is intact and then upgrade VC followed by ESXi hosts.
Please find the procedure here - http://pubs.vmware.com/vsphere-55/index.jsp#com.vmware.vsa.doc/GUID-BB6070E4-6A89-41DD-8D66-7E758A93C699.html