30 Jul
2014
30 Jul
'14
7:48 a.m.
On Jul 30, 2014, at 10:21 AM, Tom Uban <uban at ubanproductions.com> wrote:
I began looking for a USB to SCSI adapter and it
appears
that while there have been a couple over the years, they
have all been discontinued. I suppose this is due to the
lack of demand, but then when I look for used ones, they
are all (what I consider to be) ridiculously priced. What's
the deal? Does anyone have a solution for this? I suppose
an old mac or sun box and an ethernet is the solution I'll
use as I want to be able to load up images onto SCSI drives
for my PDP11 w/SCSI interface.
Well, it's a fairly niche product at this point, so not many
companies see much profit in making one. But small USB-
equipped microcontrollers which are more than capable of
handling the bus at reasonably high speeds are pretty cheap
these days, and the bus driver doesn't have to be overly
sophisticated for a slow bus; I believe the SCSI2SD just
uses 7406s for the bus driver, and its microcontroller (like
many others) has 5v tolerant GPIOs.
Another option for attaching SCSI drives, of course, would
be to buy a SCSI PCI card; there are PCIe ones, but they're
mostly Ultra320, and thus expensive (and require a chain of
adaptors to attach to 20-pin single-ended SCSI). If you
have a PCI slot, though, there are loads of low-end SCSI
cards to be had for just a few bucks. You do lose the hot-
plug benefit of USB at that point, of course.
As a thought experiment, if one were to make a SCSI USB
interface, what would be desired features? Mass storage
capability is obviously useful for being able to burn disk
images quickly and easily, but I would imagine a separate
endpoint for raw SCSI commands (and configuration) would
be absolutely essential. I'm not as familiar with USB
Mass Storage protocol as I should be, but I understand it's
SCSI-based; perhaps there's no need for a separate control
endpoint for sending arbitrary commands?
- Dave