[Simh] Overwrite last track and set badblocks

[Will Senn]

On 1/21/16 9:48 AM, Mark Pizzolato wrote:
> Hi Will,
>
> On Thursday, January 21, 2016 at 7:01 AM, Will Senn wrote:
>> A quick couple of questions...
>>
>> 1. Why does SimH prompt to overwrite the last track on some images every
>> time it runs, even if I let it, it will ask on the next run.
>>
>> 2. What is a use case for setting bad blocks and is it a one shot deal or does it
>> need to stay in the .ini?
> DEC shipped disk devices which were formatted at the factory.  Almost all
> disk media had a very small percentage of the media which didn't perfectly
> store data.  Certain modern, disk devices (MSCP) had spare sectors built into
> the internal format information on the drives and they presented a full disk
> of clean blocks to the system.  Older disks shipped with factory with a defect
> table written in the last track of the device.  When an operating system
> initially wrote file system data structures on a disk volume, it would allocate
> the defective sectors to a BADBLOCK file on the disk and therefore those
> sectors would be avoided for normal user data.  During the life of the disk
> some areas might subsequently become bad.  If the OS detected these
> later the newly identified areas would also be allocated to the BADBLOCK
> disk file and the rest of the disk could still be used.
Thanks for the explanation.
> So, back to your original question.  The prompt about "overwriting the last
> track" is intended to create an essentially empty list of defective sectors
> for a newly created disk image (for the disk types which actually had this
> 'feature').  The intention is that you should be prompted for this (or could
> provide a -Y switch on the attach command) ONLY when you are creating
> a new disk image.  If you are being prompted with this question each
> time you attach an existing disk image then there could be a bug.  Please
> identify the simulator and the specific commands which generate this
> prompt.

OK. I figured some of this out...

In RT-11v5.3 if I have the following ini section for a disk:
set rl1 writeenabled
attach rl1 storage.dsk

And I say no initially to the prompt:
Overwrite last track? [N]N

When I try to initialize the disk in RT-11, I get an error:
.initialize dl1:
DL1:/Initialize; Are you sure? Y
?DUP-F-Bad block in system area DL1:

But, if I answer Y:
Overwrite last track? [N]Y

All is good in the world. I get no errors initializing and I no longer 
get prompted at startup:
.initialize dl1:
DL1:/Initialize; Are you sure? Y

.dir vol:

0 Files, 0 Blocks
10172 Free blocks

This being the case, it appears that set badblock does not appear to be 
required. For the sake of discussion, if there is a case when it is 
required, is it a one-shot deal where the command is run in simh and 
then left out of the ini file after the bad block is created?

Thanks,

Will