How to use your ZuluSCSI RP2040 as a USB-attached SCSI controller

[rabbitholecomputing]

For anyone who might have a use case or interest in the ability to read and write to SCSI HDDs on "modern" machines/operating systems (any OS that supports USB Mass Storage Devices/flash drives), check out the latest ZuluSCSI firmware preview release, which enables most ZuluSCSI RP2040 boards to function as a USB-attached SCSI controller, allowing you to read *and write *to/from most SCSI block storage devices, such as HDDs/Zip/Jaz/MO/Syquest drives, with any modern OS/computer that supports USB Mass Storage devices. Due to hardware limitations, through is limited to around 800 kilobytes/second, but this is still significantly faster than many of the original Zip and Syquest drives that were shipped in the early-mid 90s.

If you already have an RP2040-based ZuluSCSI (red PCB), all you need to do use this functionality is update your firmware to the release at https://github.com/ZuluSCSI/ZuluSCSI-firmware/releases/tag/v2024.12.24-USB-MSC-SCSI and then remove the SD card from your ZuluSCSI, and connect your ZuluSCSI to a modern computer via USB. So far, I've tested this against a handful of different SCSI hard drives, a Zip drives, an AppleCD 300i CD-ROM drive, and a much newer Plextor SCSI CD-ROM drive. Tape drives are not supported at this time, as implementing support for emulating the tape transport commands requires additional effort and testing to get working reliably.

DVD-RAM drives should also work, but have not been tested. If you try it out and have questions about this feature/functionality, please ask them at https://github.com/ZuluSCSI/ZuluSCSI-firmware/discussions/491

Initiator-capable ZuluSCSI models​

• All Full-size ZuluSCSI RP2040 boards
• Full-size (desktop) ZuluSCSI Pico (OSHW) board
• ZuluSCSI Compact RP2040 Rev 2023b - available for USD $52
• ZuluSCSI Compact Homebrew Rev 2023b - a through-hole-only kit version, available for USD $42.42

ZuluSCSI models that do not support initiator mode​

• All ZuluSCSI V1.0/V1.1/V1.2-based boards (blue PCB)
• ZuluSCSI Pico Slim (DB25)
• ZuluSCSI Mini
• ZuluSCSI Compact RP2040 Rev 2022a

 

[rabbitholecomputing]

There's also an operational USB serial console that logs some basic information about what is going on, which you can connect to using any terminal emulation app. The output will show you the device it detects, as well as quasi-real-time calculated transfer/throughput rates, and any errors it might encounter. You can purchase an off-the-shelf power supply to power any external drive with a four-pin Molex power connector for about $12. Sparkfun sells the TOL-15664 for $11.95, and Digi-Key also stocks and has them for sale for $12.50, at https://www.digikey.com/en/products/detail/sparkfun-electronics/TOL-15664/10650708

 

[Realitystorm]

I will need to test this with Basilisk II. I used to use Basilisk II and my USB zip drive to setup disks, with this, I should be able to setup my SCSI zip and Jaz drives using Basilisk II.

 

[rabbitholecomputing]

I'm pleased to report that in the days since this initial announcement, this new functionality has been improved upon significantly, and has now been incorporated into the v2025.01.09 firmware release, the first ZuluSCSI firmware release of 2025. This release supersedes the previous preview release.

 

[aplmak]

Can you connect let’s say an Archive 2150S tape drive and have it copy the tape? This would be a neat feature to archive old tapes…

 

[paws]

I don't remember to what extent I've bothered you about this before, but: There once was a protocol for called SMDI for SCSI-equipped samplers (musical instruments) that allowed moving sounds between the sampler's RAM and a program on a computer. So you could record something into the sampler, load it into the audio editor on a computer to edit on a nice big screen, and then send it back.

If a plug-in could be made for, say, Audacity that supported this, I think a lot of musicians would be very interested. But I'm not sure what the USB interface would look like. Would it require extensive firmware support?

https://www.exellon.net/book/smdi.pdf

 

[rabbitholecomputing]

@aplmak SCSI tape drives are not supported in initiator mode at this time. While there's certainly no purely-technical reason why you couldn't implement this in the firmware, it's just not as easy as it may appear on the surface, since the SCSI command set for tape/streaming devices is an additional specification, because there are commands for controlling the actual tape transport mechanism which are specific to SCSI tape devices.

Furthermore, many QIC tape drives such as the Archive Corp. 2107S will need to be inspected and/or serviced before they will operate reliably these days, because the rubber belts can and do disintegrate and/or stretch out, and therefore require replacing before you can safely attempt to recover data from an old tape. Archive Corporation has not existed since 1992, which is when Conner Peripherals acquired the company.

From a cursory online search, it would seem the 2107S dates from 1987, so age of an Archive 2107 tape drive is going to be in the 33-35 year old range, and will almost certainly require refurbishment prior to being deemed reliable enough to confidently attempt reading of a tape of this vintage. Lots of things can and do go wrong when it comes to any sort of 30+ year old mechanical tape transport mechanisms. It's important to have confidence that the mechanism is actually reliably working prior to attempting to simply dump a decades-old tape, because you may only get one or two attempts at doing so before the oxides on the tape delaminate from the mylar backing, if they haven't already.

Quoting from https://www.edn.com/the-qic-and-the-dead/

The hobbyist community has developed a wide variety of homebrew capstan repair procedures involving dipping plastic, rubber tubing, silicone tape, or rubber O-rings. However, the tape cartridges fail as well. After decades of storage, the oxide delaminates from the backing Mylar tape and falls off, usually contaminating the tape head with oxide flakes in the process.

 

[shirsch]

From my experience, drive issues pall in comparison to degradation / failure of the tape cartridge itself. The internal tension belt on most tapes will have already failed or will do so destructively the first time you try to read it. Even tapes from the 90s that are factory sealed are likely to be bad. Ask me how I know all this.

I've yet to see a bad belt in an Archive drive, but the pressure roller is certain to have melted into soft goo. I've replaced a couple of them them with Chinese replacement roller wheels intended for tape decks. It's a major PITA and yields mixed results. Tandberg drives age far better than Archive / Wangtek, mostly just needing cleaning.