I have 2 zip ide drives hooked up on 2 amiga4000.
Both are installed with amigaos 3.9.
One on a ide-fix adapter and one on the internal ide port.
Only way I got to work them reliable is with idefix.
The mountlist entry and hdtoolbox may work but just for once.
Once you move in un other disk it's trouble.
Idefix is slow(400KB/s) but works always and that is better then not working at all or crashes etc...
First install idefix and then do a formatls120 it works!!!