On Wed, Feb 20, 2019 at 9:21 AM Glen Slick via cctalk <cctalk@classiccmp.org> wrote:
> On Wed, Feb 20, 2019 at 8:57 AM Charles Anthony via cctalk > <cctalk@classiccmp.org> wrote: > > > > However, in the original posters case, the SIMH disk image is being > copied > > to the RA81 drive without the benefit of the MSCP controller (if I > > understand correctly). This would lead to track misalignment and could > > result in the observed behavior. > > How could you possibly write to a real RA81 drive without going > through a real KDA50 or UDA50 MSCP controller? Nothing like that is > happening in the original post. Just the disk size was chosen to be > that of an RA81, and the issue is to exactly match the emulated disk > size to that configured by the hardware, which is an MSCP SCSI > controller and drive in this case. > Re-reading the original post, it it not clear to me how the disk write was accomplished; I am not familiar with the mentioned hardware. If the data was written to the RA81 with a controller that correctly did the spare sector mapping, then my spare sector hypothesis is wrong. The reported symptoms sound like a disk geometry issue; the data passes through several systems on the way to RSTS, and it seems likely to me that one of the steps is damaging the data. As I lack experience with or access to the specific hardware, I am speculating about the exact failure mode. I do however believe that it is highly likely that disk geometry is the root of the problem. Having no no further specific ideas about the failure mode, I will shut up now. -- Charles