I just upgraded our lab Nexus 1000v from 1.4 to 1.5. Before the upgrade I assumed that it be like the upgrade from 1.3 to 1.4 where you first had to upgrade the VEM modules on each ESX host and then upgrade the VSM.
Fortunately I didn’t just jump right in and go on those assumptions. I took a few minutes to look through the Nexus 1000v Install and upgrade guide – http://www.cisco.com/en/US/docs/switches/datacenter/nexus1000/sw/4_2_1_s_v_1_5_1/install_upgrade/vsm_vem/guide/n1000v_installupgrade.html
I am glad I did because when going from 1.4x to 1.5 the VSM is upgraded first and then the VEMs.
I was also pleasantly surprised to see the VSM upgrade is now similar to upgrading the other Nexus products by using the “install all” command instead of the GUI upgrade app that was used when going from 1.3 to 1.4.
The bad news is if you are still on VSM/VEM 1.3x it is a 2 step upgrade to get to 1.5. You must first upgrade to 1.4a and then upgrade to 1.5.