PDP-11 disk image question

[Glen Slick]

On Sat, Feb 16, 2019 at 1:20 PM Bill Gunshannon via cctalk
<cctalk at classiccmp.org> wrote:
>
> I have a CQD=220A/MT configured for 6 disks and one tape.
> As for disk types, you can toggle RA ON or OFF on each drive.
> You can specify one RA type that will be in effect for any
> disk with RA ON.  Types are: RA70, RA80, RA81, RA82, RA90 and RA92.

Looking at this further, I don't believe the CMD CQD RA type option
does what you think it does. I don't believe it has any effect on the
reported geometry of the MSCP unit, I believe it only changes the
reported type name of the MSCP unit.

I need to change the firmware on one of my CMD CQD controllers to a
version of the firmware which has both the RA type specification
option and RA type toggle per unit option to verify the actual
behavior myself.

I tried firmware version REV. B3A-00 on a CQD-220/TM which has an "A =
Report specific media type" option, but not a "1 = Toggle device RA"
option. With that firmware specifying an particular RA type had no
effect on the reported unit geometry.

I have firmware version REV. B2L-00 I can try on a CQD-420/TM which
has both "A = Set the RA number" and "1 = Toggle device RA" options. I
currently have firmware version REV. B2C-00 on my CQD-420/TM which has
neither of those two option.

Regardless of that, there are a couple of options you can try:
(1) Find out the exact unit size that is being reported in your
configuration with your CMD controller and hard drive, and configure
the emulated hard drive unit size to match that.
-or-
(2) Reconfigure the SCSI hard drive independent of the CMD controller
to match the exact unit size of the emulated hard drive. Then use the
SCSI hard drive as a single unit without partitions on the CMD
controller and it should yield the desired result. To reconfigure the
SCSI hard drive you can use sg_format from the sg3_utils to soft
resize the reported capacity of a SCSI hard drive down to a lower
limit. I have done that several times, for example to resize a 9GB
drive down to 1GB in capacity for systems while can't handle drives
larger than 1GB. The sg_format command with the -resize option doesn't
actually format the drive, it just uses some mode page commands to
change the reported drive capacity.