How to determine whether an ESXi 4.1 host was previously upgraded?

[JShroll]

A client of mine is seeking to upgrade some vSphere ESXi 4.1 hosts in remote offices using Update Manager.   Virtual Machines are located on Local Storage. 

Update Manager seems to be the logical choice here, as an interactive upgrade via Dell DRAC is not possible.  However, I'm seeing that the upgrade to 5.1 won't work if the 4.1 host was previously upgraded from 3.5.

My Linux knowledge is sparse, but there is probably a way to view the current partition layout via Unsupported Mode or SSH that could reveal this?  

[a_p_]

You can run fdisk -lu from the command line to check the partition layout. If you see two 250MB partitions you are ok to upgrade. Take a look at e,g, http://blogs.vmware.com/vsphere/2011/08/esxi-and-lopsided-bootbanks.html for how the partition might look like (lopsided bootbanks) if the system was upgraded from ESXi 3.5.

aNDRÉ