A little while ago I wrote about unsupported scenario of upgrading NX-OS on Nexus 7000. It’s a scenario I found few months ago and forgot to write about it, but my other customer had same problem few weeks ago which refreshed my memory. Back then we got information from Cisco TAC that this scenario is not supported but no official information is available about this.
I got mail from Andras Toth from Cisco TAC lately pointing me that this limitation has been documented in NX-OS 5.1 release notes. Thanks Cisco for making it clear. And remember it applies to all NX-OS releases, not just 5.1.