Law enforcement does not require a search warrant, in your hypothetical, for 2A precicesly because the search of 4B leaves the residence of 2A unmolested. I do not believe the metaphor falls apart, at all: because the virtual 'tenant' vhd0 of physical hard-drive hd0 cannot be undisturbed by the search and seizure of the data in virtual 'tenant' vhd1--and might reasonably be considered to have the data subjected search and by definition seizure--law enforcement _should_ require a warrant for vhd0 and vhd1.

Going back to your hypothetical, if the resident of 3A were stuffing materials of interest into the crawlspace between their ceiling the the floor of 4B and said crawlspace could only be accessed through the floor of 4B, the interested authorities would need either the express permission of the residents of 4B for entry into their residence or a warrant for search. _That_, I assert, is a similar situation akin to the topic under discussion.

In the case of Pinboard, at least, they had their own machine(s), i.e dedicated servers not virtual servers or shared hosting. So at least some machines were taken the belonged entirely to people not subject to the warrant - it seems like the idea was just to take the whole rack, regardless of who else was on it.