I'll make amends for suggesting that it might be an ESDI drive.
My secret stash of IBM documentation calls the interface "Direct Bus Attach", so it is neither ESDI, SCSI or IDE. It directly attaches tot he system on the MCA bus, but presents itself as an ESDI drive logically. They were used in the model 50Z, 55, and 70.
For the purposes of this thread it really doesn't matter what it is, as it's still an oddball that can't be moved to another system to be imaged.
FWIW, if you look hard enough you can find instances where IBM used "ESDI" to describe the drives, like,
this announcement letter for the PS/2 Model 70 has this one (presumably slightly garbled) sentence in it:
The 80386 processor models 081 (80 million bytes/20MHz), 161 (160 million bytes/20MHz), A81 (80 million bytes/25MHz) and A16 (160 million bytes/25MHz) enhance ESDI files and support the addition of an 80387 optional Math Co-Processor, which offers significantlyimproved system performance for a desktop environment.
(The announcement for the P70 does not have the word in it.) There is also
this maintenance manual (published well after the machines were not on sale anymore but still being supported in the field) that refers to the drives as "ESDI":
1 30MB Hard Disk Drive (ESDI) 6128287
(Includes ESDI hard disk controller)
1 60MB Hard Disk Drive (ESDI) 6128294
(Includes ESDI hard disk controller)
1 120MB Hard Disk Drive (ESDI) 6128291
(Includes ESDI hard disk controller)
But notably the parentheses indicate that the drives have integrated ESDI controllers, IE, they're not "normal" ESDI drives. Also, this is not a technical reference manual, it's a service manual for parts-swapper drones that just need "a name" for the part they're looking for. Outside of these sort of very rare references there is very limited evidence that IBM referred to these drives as being anything other than "fixed disks" or "DASDs", the interface/technology was not something they really advertised and none of the actual technical manuals
including this very complete "DASD Storage Interface Specification" reference describes anything about the interface or the API as "ESDI".
Long and short of it is, yeah, they "look like" ESDI drives logically but the interface is nothing like a normal ESDI drive, so it seems kind of wrong to call them that; specifically for the purposes of this thread if you call them ESDI it might raise false hopes that someone could somehow hook these drives up to a ESDI controller in a generic machine or connect a generic ESDI drive to their PS/2 with some kind of adapter cable. But on the flip side, if you're searching specifically for a PS/2 drive there's a non-zero chance it'll be described as ESDI instead of or in addition to "DBA" or whatever, so, eh, there's no way to win.
Ultimately I guess it doesn't matter what you call them in discussions as long as it makes clear that they're
proprietary and therefore you're pretty screwed. Ultimately the whole point of this interface was to make it difficult for PS/2 customers to buy drives from anybody but IBM so it's not surprising there was never an official popular name for it.