There are old threads about this on Appelfritter. Here are the basics:
SCSI-USB adapters do exist, and they do work under OS X, with the following qualifications:
(1) You can connect only one SCSI device at a time - even if the adapter says multiple SCSI devices can be daisy-chained.
(2) The SCSI ID of the external drive MUST be set to zero. This is clearly related to why you can only use one device at a time, even though you can daisy chain them under OS 8/9 and some versions of Windows. As an FYI, if you set the SCSI ID to something other than zero, the device will show up multiple times on the desktop. For example, if you set the ID to 3, it'll show up as 4 identical drives on the OS X desktop.
(3) The SCSI device must be terminated AND supply termination power. This is key. Most external hard drives supply term power, but not all. And especially with an older Apple external HD, you probably have to attach an external terminator.
(4) As the above indicates, this will only work if the SCSI device has an ID selector that you can set to 0. That rules out ZIP drives (which IIRC only allow you to select 5 or 6).
As for brands, only Adaptec ever claimed to allow daisy chaining - and therefore escape the "SCSI ID set to zero" requirement - under OS X. But unless you can find one in a closet at $WORK
they're very rare and expensive.
More common are the Microtech adapters, and they work fine with the above caveats.
Good luck - though
SCSI-USB adapters do exist, and they do work under OS X, with the following qualifications:
(1) You can connect only one SCSI device at a time - even if the adapter says multiple SCSI devices can be daisy-chained.
(2) The SCSI ID of the external drive MUST be set to zero. This is clearly related to why you can only use one device at a time, even though you can daisy chain them under OS 8/9 and some versions of Windows. As an FYI, if you set the SCSI ID to something other than zero, the device will show up multiple times on the desktop. For example, if you set the ID to 3, it'll show up as 4 identical drives on the OS X desktop.
(3) The SCSI device must be terminated AND supply termination power. This is key. Most external hard drives supply term power, but not all. And especially with an older Apple external HD, you probably have to attach an external terminator.
(4) As the above indicates, this will only work if the SCSI device has an ID selector that you can set to 0. That rules out ZIP drives (which IIRC only allow you to select 5 or 6).
As for brands, only Adaptec ever claimed to allow daisy chaining - and therefore escape the "SCSI ID set to zero" requirement - under OS X. But unless you can find one in a closet at $WORK
they're very rare and expensive.More common are the Microtech adapters, and they work fine with the above caveats.
Good luck - though