You believe, or know?
I've talked to guys who run Windows on servers stored on NetApp clusters.
If they upgrade SERVERA from Win2000 to Win7 it's down. Period. There's
no running SERVERA on this cluster while you upgrade SERVERA's OS
partition on the other cluster.
With Mimix, I would normally upgrade PRODBACK to 7.1 while PROD was still
running 6.1. Then switch from PROD to PRODBACK and upgrade PROD. When
that's done, switch back to PROD. Why that order? Save/restore previous
release concerns. Granted, I had already upgraded SANDBOX to 7.1 and
tested the applications on that first.