Hello;
My experience are the following may be not best way but it is running :
Firstly remove secondary fabric and update master fabric(bootrom and application) and reboot the chasis for restarting new image If everything went right shutdown the chasis remove the master fabric and insert slave fabric ( with old image ) and repead same procedure. When two fabric image version are the same insert two fabric and restart all chasis. Finally You may update I/O module boot code .
Warning!!!: Please read carefully minimum requirement about fabric and I/O module bootcode version for new version image.
I applied this method because if there was a problem about master fabric when software update at least i would have one working(Old imaged Slave Fabric) fabric :)
Best Regards
AYDIN KOCAK,
3COM Enterprise LAN Expert ( Pre & Post Sales),
TippingPoint Security Engineer,
CCNA,CCDA, CCIE R&S Written