I use many old parallel SCSI(-1/-2) devices (many "Fast SCSI-2", 10MB/s, 8 bit wide), which I want to attach to a modern computer via a classic Adaptec PCI SCSI host adapter in "target mode". It should emulate an HD drive of arbitrary size (or better: multiple devices at once). The data lives in image files on real HDDs or RAM.
I've crawled through the web to find any helpful information to make a (probably simple?) goal reality. While it seems that both GNU/Linux and FreeBSD offer such possibilities and also seem to be configured quite easily, there's a serious lack of documentation / man pages here. The two or three proposals I've found online and tried in my local setup all didn't work. So, after weeks of trying, I thought it might be good idea to put my problem here and directly ask professionals.
What I'm NOT after: Anything iSCSI and network target stuff - this is about vintage computing. I know of several different (mostly hardware) solutions, including SCSI2SD, ACARD converters and so on, but those are not providing what I want. I also don't want any kind of embedded solution, hardware hacks etc. - the only solution I'm interested in is the one described above: SCSI card & PC & free / open OS (no Windows solutions for me, please - but you may put them here for others). There's a (rather hacked-together-ish) tool ("scsi_target" IIRC) with free code, that's quite unstable in the long run and slow, too - that's no suitable solution.
What I have: I have an IBM PC with a suitable Adaptec AHA-2940/SE card supporting "target mode". It is also activated in it's BIOS extension and has been given a host ID there. (Open to alternative PCI parallel SCSI host adapter card recommendations if this one was a bad choice) The hard drive contains a recent FreeBSD with a custom kernel (with all modules activated that support / are required for "target mode" SCSI) and a recent headless Ubuntu with SCST.
I got none of those solutions working.
Related links to resources I followed, tried or read only to learn from: https://www.vogons.org/viewtopic.php?t=66955, http://web.archive.org/web/20141021111304/http://www.tenox.net/docs/scsi/the_programmers_guide_to_scsi_brian_sawert.pdf, and http://scst.sourceforge.net/
Common problems: Unfortunately, but naturally of course for this tech, there's some confusion - while searching for information with keywords "Target" / "Target mode", I get lots of hits in the iSCSI-Bubble, which is not my topic here. Even when adding "parallel scsi" / "pscsi". There's a "pscsi scst extension" mentioned on their massively outdated website, but I didn't find anything related to it, apart from some unfinished stuff. By tendence, it's unclear how to write up the config files; often lacking information about options, possible values, their meanings, etc. I lack some knowledge on commands / tools to use for debugging, monitoring and scanning scsi bus and whether the software is configured correctly, too. I also often don't know how to find the correct SCSI bus location (like 1:3:0:0 or only 3:0:0 - I know it's bus:target:lun, but how am I supposed to count / find out / be sure, and what's the first digit on a 4-number path?).
I'd appreciate gaining some knowledge here, getting helpful answers and possibly see some of you put up setup instructions and different example config files for mentioned frameworks / OSses to learn from and eventually get a working system.
Thank you for your attention and stay safe!