I have a 2-node vSAN cluster with Dell r730xd hosts, running ESXi v7.0. I put one of the hosts into maintenance mode today, to start updating them both to 7.0b. When I tried to run the update from vCenter, it stopped with an error and checking the esxupdate log made it seem like something to do with the bootbank not being found. The host has ESXi installed on SD card via the Dell Dual SD Module. iDRAC shows both SD cards in the mirror to be healthy and working normally.
I rebooted the host, and it does seem to boot okay, and comes back online to vCenter but now shows that "No coredump target has been configured. Host core dumps cannot be saved." and trying the update again still produces same error in esxupdate log. I really am still learning vSphere but I would deduce something is wrong with the bootbank partition on the SD card, even though the system still boots okay... I even tried to use a 7.0b ISO USB installer to upgrade ESXi but when the installer gets to scanning devices, it quickly produces some error about "UnicodeDecodeError" and not being able to "decode byte 0x99 in position 5" because of "Invalid Start Byte". I'm guessing when the installer is scanning the SD cards to find existing ESXi, whatever bootbank issue is there causes an error out on installer booting from USB stick.
Either way, what can I do to check into why I am suddenly having what seems to be a bootbank issue and can I repair it somehow?