[rescue] SCSI2SD v5.1 in a SPARC Classic

[Patrik Schindler]

Hello Alan,

Am 11.01.2025 um 22:20 schrieb Alan Perry via rescue <rescue at sunhelp.org>:

> FYI. Even when it wouldn’t boot from the SCSI2SD probe-scsi worked.

This might be because simple device detection is AFAIR done with asynchronous SCSI transfers, while actual data moving utilizes faster synchronous modes.

I think alike to Jonathan Katz, and suspect you had a termination issue. Golden SCSI rule: The *ends* of the chain must be properly terminated. See remark from Chris T.

I know that older Macs are notorious to not obey this rule. The internal hard disk is terminated, and there is no termination on the mainboard. This works because the internal cable is comparably short. And there is no need to come up with some magic to see if an external connector is attached or not (to enable/disable termination onboard).

Guesswork: Maybe the Classic also has no onboard termination? When you plug in your CD drive, the whole chain was terminated correctly. When you unplugged it, that was no longer the case. Maybe the SCSI2SD is more sensitive in terms of noise on the bus.

Such issues are preferably solved by an external terminator, or worked around by lowering SCSI transfer speeds, if this is configurable.

:wq! PoC