Unpresenting the ESX host in the EMC Unisphere before the Upgrade ?

Hi folks,

I'm in the process of upgrading manually all of my ESX 4.1 into ESXi 5.1 Update 1 hosts in the Data Center using interactive upgrade by inserting the .ISO file into the iLO console, in regards to the slow ESXi boot process:

1. Is it necessary to unpresent the ESX / ESXi host from the FC Storage Array config (in this case EMC Unisphere) before the upgrade ?

2. what should I do to ensure that all of the existing production ESXi host boot up quickly without causing any LUN missing or causing any VM downtime by doing the step #1 above ?

Any kind of help and suggestion would be greatly appreciated.

Thanks