Older SCSI hard drives take over 3 minutes to mount.

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Older SCSI hard drives take over 3 minutes to mount.

OK, this experiment I'm doing is just for fun, so no need to drift off into "Why do you want to do that?" comments, please. :)

I've recently obtained and SCSI to USB adapter and have been messing around with older SCSI devices to see what works with a modern Mac. It has a SCSI-2 50 pin connection. Devices like ORB drives and Jaz drives work perfectly and mount within a couple seconds. The only hitch is the SCSI ID has to be set to zero.

Next I moved on to an older hard drive that has the older, SCSI-1 Centronics connecter. I bought a SCSI-1 to SCSI-2 adapter, then plugged in my USB adapter. The hard drive is also terminated properly. The drive is formatted in FAT.

So, when I connect it to my 2017 27 inch iMac running Catalina, it takes exactly 3 minutes and 30 seconds for the drive to mount. I also have 10.12 and 10.5 Server virtualized. It takes exactly 3 minutes and 30 seconds on each of those to mount as well. I have also connected it to my iPhone running iOS 13 with the Lightning to USB 3 adapter, and it takes exactly 3 minutes and 30 seconds to show up there as well in the Files app.

Here's where it gets interesting. I also have Windows 7 and 10 virtualized, as well as the Haiku OS. On all three of these operating systems, the drive mounts immediately, just like one would expect. This is on the same Mac, using the same USB port.

Reformatting and repartitioning the drive to HFS+ or APFS works perfectly, but doesn't change the 3 minutes and 30 seconds delay.

I understand that macOS and iOS share code base, but their processors and radically different in architecture and speed. And yet, the 3 minutes and 30 seconds is constant between these two types of devices.

So....my question obviously is, what's magical about 3 minutes and 30 seconds with older SCSI-1 devices on Apple's operating systems, and why is this not an issue on Windows, even when hosted on the same hardware and USB port?

Posted on Dec 3, 2019 11:48 AM

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Answer 1

Dec 3, 2019 1:45 PM in response to niles32

You’re going to want to scrounge a SCSI bus analyzer, maybe also a USB analyzer, and find out what’s going on. I would suspect either USB or SCSI bus scans, or bus or device or command timeouts, or a combination. Different operating systems use different sets of commands. The analyzer will tell you what this contraption is doing, and what it’s being asked to do. (As you’re probably aware, USB is arguably SCSI with random disconnects, too.)

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Answer 2

niles32 Author

Level 1

8 points

Dec 3, 2019 2:12 PM in response to MrHoffman

Well, the USB Adapter works fine with ORB and Jaz drives on the Mac and iPhone, so I don't think it's particularly the issue. The SCSI hard drive is an Apple one, and works fine on SCSI based Macs. There's nothing particullary exotic about any of this.

It's definitely something with the software of Mac OS X (and its derrivirates in the iOS). The adapter shows up right away under the System Report and with using the "ioreg -p IOUSB" command....just no volume. Nothing in the Disk Utility either until it actually mounts. In addition to being curious about the magic 3:30 number, I'm interested if anyone knows any terminal commands to essentially "goose" the USB bus into looking for devices.

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Answer 3

Dec 3, 2019 3:29 PM in response to niles32

The SCSI and USB commands used, and command responses, and sequences, and options, can be wildly different across platforms. Even across versions of the same platform. Different adapter vendors had various cores.

Just because the controller works for some devices and not for others... is pretty typical of SCSI, particularly when you’re dabbling in older SCSI. There was this old and adorably misguided idea that two SCSI disks were interchangeable, back then. UltraSCSI was fairly compatible, but the further back in SCSI eras toward SCSI-2 and SCSI-1 and narrow and wide, and vendor divergences and variations such as DSSI, well, the more differences and incompatibilities can and would crop up.

Adaptec SCSI controllers seemed to use the same firmware core with the same oddities, updating the hardware support and oddities for newer-generation SCSI controllers. Different SCSI devices have different firmware stacks, as well. Same for the storage device and storage controller vendors. Firmware and processors all over the place.

Some old SCSI disk devices needed firmware updates to avoid device hangs and crashes—you‘d often then have to re-boot the host to un-wedge a crashed SCSI device—and the SCSI host driver developers of some operating systems spent years learning and adapting and updating drivers to the observed behaviors of the connected devices, too.

Short an analyzer, what’s happening requires source code access to the SCSI stacks in the hosts. And even then, an analyzer is very handy as SCSI devices don’t always respond as expected.

SCSI itself is pretty wild, too. There were provisions for and variously examples of SCSI connected terminals, image scanners, printers and other now-long-gone devices. USB didn’t arise from anywhere, well, strange may not be the best word here. The history of T10 and T13 committees can certainly be interesting to some folks, and ir’s all on a path to USB, SAS/SATA, and other buses.

Unless you get really lucky around here with somebody that’s run with this particular combination of hardware, you’re headed for a bus analyzer, for either or both of USB and SCSI, and a look to see what’s actually going on with commands and responses.

ps: SCSI is known as “scuzzy” and not “sexy” for a reason.

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Older SCSI hard drives take over 3 minutes to mount.

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