DataStore conflicts with an existing DataStore in the DataCenter – Manually disabling Storage I/O Control
I ran into this issue yesterday while reconnecting hosts in our vCenter Server following a complete reinstall - the reasons for which are a long story, but suffice to say that there were new certificates and the host passwords were encrypted with the old ones.
The LUNs had been unpresented at the hardware level by the storage team, but had not been unmounted or removed from vCenter. This is *not* the way to remove storage - let me re-iterate: remove storage properly. Unfortunately in this case the storage was removed badly - doing this can lead to a condition called "All Paths Down" or APD which is best explained by Cormac Hogan (@vmwarestorage) in the article Handling the All Paths Down (APD) condition.