PDP-11 disk image question

Paul Koning paulkoning at comcast.net
Sun Feb 17 13:32:46 CST 2019

> On Feb 16, 2019, at 1:04 PM, Bill Gunshannon via cctalk <cctalk at classiccmp.org> wrote:
> ...
> First, my hardware.  I  have a PDP-11/93 with a CMD SCSI Module and
> a BA350 with 6 2GB hard drives.  The Module is set up to present RA81
> disks and the first 3 disks have 4 partitions each which should work
> out to 12 RA81 disks. (But that last part is unimportant right now!)

A real RA81 has 891072 blocks, i.e., it's 445 MB.  If your partitions are indeed 1/4th of a 2 GB disk they may be just over 512 MB.  If so, your RA81 image is not valid for those partitions.

Try shrinking the partitions to be the actual RA81 size, or slightly larger.

By the way, another possible issue: the free space bitmap in file SATT.SYS is created at pack format time to be large enough for the number of clusters on the disk.  If you move the image to a bigger disk, even one with the same device cluster size, it may be that the number of pack clusters now exceeds what SATT.SYS describes.  That too is an invalid file system.  I would expect that to give a more explicit error message, but it may be that this doesn't happen in INIT, or not at this stage.

Either way, the short answer is: RSTS will object to file systems moved to a smaller destination, or to one that is too much larger.  What is "too much" depends on a number of details.


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