RaSCSI is a virtual SCSI device emulator that runs on a Raspberry Pi. It runs in userspace, and can emulate several SCSI devices at one time. There is a control interface to attach / detach drives during runtime, as well as insert and eject removable media. This project is aimed at users of vintage Macintosh computers from the 1980's and 1990's.
It's aimed at vintage Macintosh, but wouldn't it work with any old computer using SCSI?
I have an HP machine that I would be happy to resuscitate with a new install of HP-UX, but its CD drive is dead.
https://github.com/akuker/RASCSI