Hey Chris,
ESX/ESXi actually does a scan and discovery for datastores and LUN's during boot.
This can be seen in the boot.gz file that is populated in /var/log of the ESXi 5.x hosts. So it does not need to do another rescan immediately after boot!
Are you seeing any issues with the LUN's not detected on first boot? Also what version of ESX/ESXi are you running?
Thanks
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