ESX host does not discover new path after migrating to new fabric

Once, I work on fabric migration.  They want to migrate to new equipment and choose not to link the existing and new switch together (no ISL) to have a clean config in new fabric.  The servers connect to different fabric A and B.  On each migration, we need to re-connect storage controller on one fabric and the servers that are connecting the controller to new fabric at the same time.  Only one fabric and one controller will be worked on each time.  Since they are all ESX hosts and no AIX, it is much easier. We complete the job in the weekend during low I/O period.  What happens is after connecting to the new switch, it does not see the new path even VI team rescan.  I did confirm zoning had been completed correctly on the new fabric.  They suggest me to follow VM article Configuring fibre switch so that ESX Server doesn't require a reboot after a zone set change


However, I know RSCN is enabled in the Cisco switch.  Eventually, VI agree to vMotion the VMs in the host, and reboot the ESX host, one by one.  After that, they are discovered correctly. 


One thing we learn, stay away from boot from SAN for ESX host, it takes 30 min for each host to come up after reboot even there are not a lot of luns in the ESX clusters.  It is proven much faster to boot ESX from local disk. 


Also, minimize the number of RDMs!!!  I work in another messy environment with lots of RDM.  Even rescan cannot happen during business hours.