Meaning attaching old SCSI drives to modern Macs, not putting SSDs into old Macs.

GBSCSI and ZuluSCSI support “initiator mode” that can be used to either image an attached SCSI disk to a file on an SD card or provide live access to it over USB as a mass storage device—with better performance than the old USB 1.1 SCSI adapters too, which top out at about 750KB/sec.

If you just want to grab the data to put into a more useful format, as opposed to really needing to actually use them as drives on your modern Mac, you may be able to do it if you happen to have access to something that has a couple dozen GPIOs, works with 5V logic, and is running faster than 1 GHz.

An RPi would be perfect except they use 3.3V logic. There are ways to deal with that such as bidirectional level shifters, such as [1].

Anyway, if you can find such a system bit banging SCSI on the GPIOs should work. Heck, on the original Mac Plus SCSI it was partly bit banged and that was on an 8 MHz 68000 where each instruction took at least 4 clock cycles.

They used an NCR 53C80 SCSI chip which pretty much simply provided registers to read and write the SCSI signals, plus a little bit of logic to handle those few places where something too fast for bit banging was needed.

Looking at my copy of the SCSI 2 spec briefly, it looks like the only thing you might have to worry about is the spec requires at most 10 ns difference in propagation delay between any two signals between the two ends. If you needed to change multiple signals together and used some higher level interface that did them one by one that might be slow enough it would look like propagation delay to the other end.

That could be addressed by directly writing to the registers that control the GPIOs. On most system each register controls multiple GPIOs and you can change them simultaneously. With SCSI we'd be using enough GPIOs that we might have to write to 2 or 3 GPIO control registers, but that would probably be fine.

It looks like the next shortest maximum allowed time is 400 ns. Way too short for an 8 MHz 68000, but trivial for a Pi or similar.

[1] https://www.adafruit.com/product/395 or https://www.sparkfun.com/sparkfun-level-shifter-8-channel-tx...

I would use a mac of the Beige G3 variety. They still had SCSI ports and can run a bunch of OSes. I'd dump to a BlueSCSI or make a network disk that can be read by a newer OS or host a share from a newer computer to dump onto (SMB, AFP).

Another good candidate for hardware is a Lombard Powerbook. Otherwise you'll need an adapter.

If you've got a mac with a pci-e slot, you can get a pci-e card off ebay and an appropriate stack of adapters to go from a modern wide cable to whatever you need? If you don't have a mac with a pci-e slot, borrow a desktop pc with a slot and go from there? If you borrow an old enough desktop with PCI you might be able to get an older scsi controller and skip a few chains in the cable adapter path.

Or using the bluescsi initiator mode to make a disk image seems not too badly priced either.

There are some Firewire SCSI adapters. Sometimes older Firewire tape drives have internal SCSI to Firewire boards. I've used them to with old SCSI CD drives.

This post is about using a SCSI scanner but it seems to validate the SCSI->FireWire->Thunderbolt idea.

https://catspawdynamics.com/ultra-scsi-to-firewire-to-thunde...

Amazon has usb scsi adapters, I dont use apple devices, but i'd guess that would work. https://duckduckgo.com/?q=usb+scsi+adapter&ia=web

If the reason to connect them is to dump them, something like https://bluescsi.com/ in Initiator Mode might work: https://bluescsi.com/docs/Initiator-Mode

If you need to connect them physically, I think you're blocked by HBA chipset support in macOS.

There is a path, but it's not what I'd call "good". Thunderbolt to Firewire to SCSI. It's a dongle Rapunzel and you're reliant on device enclosures for power.

May be better with a native PCI-e or PCI HBA and 700W power supply and a junker ATX Linux machine to provide network shares.

very much not on topic, but that reminded me: my first PC (286) miraculously had a 40MB 2.5" Apple-branded HDD connected via SCSI adapter. Who knows where it was sourced from. One weird thing was that it initialized on boot for about 40 seconds, displaying nothing. I've been really surprised later seeing how fast other PCs with ATA drives were to boot. I still wonder, and maybe someone has a clue why init was so long? Is it something inherent to SCSI?

https://github.com/PiSCSI/piscsi

Get yourself a board, raspberry pi, and set up a samba server.

Here's a solution to the opposite problem: https://bluescsi.com/

Use any other kind of PC with an expansion bus to dump the blocks to a modern block device, then attach that to the Mac.