[Info-vax] Exploring a hard drive on a new Vaxstation

[Johnny Billquist]

On 2018-01-29 20:26, Stephen Hoffman wrote:
> On 2018-01-29 19:09:00 +0000, Rod Regier said:
> 
>> The 21 bit addressing limit could give you "interesting" issues.
>>
>> As long as the blocks needed for the *boot* were low addresses on the 
>> drive, you could use a very large drive.
>>
>> But heaven help you if the needed blocks ended up on high addresses. 
>> In that case, the game was over unless you performed a dump/reload for 
>> the data to push those blocks back down again.
> 
> 
> Boot failures are rather more benign than what can happen here with 
> VAXstation 3100, MicroVAX 3100 models 10 and 20, and MicroVAX 3100 
> models 10e and 20e below console VMB V6.4, when configured with a boot 
> disk larger than ~1.073 GB.
> 
> The system dump will corrupt the system disk on crash, just as soon as 
> one or more of the extents of a dump-related file happen to be located 
> or relocated out beyond 1fffff (base16) blocks.  The write I/O will wrap 
> around.
> 
> That wrap will stomp on some matching lower-addressed range of disk blocks.
 >
 > That's a corruption which can make any subsequent system operations
 > rather less than entirely reliable, too.

Right. The crash dump done through the rom driver is another potentially 
dangerous detail, and indeed one with potentially much more dire 
consequences than the booting issue itself.

> Data disks have different and larger addressing limits, and those limits 
> based on the particular VMS or OpenVMS VAX version in use.

"Data disks"?
The limit is just one of the device driver that exists in the boot rom. 
The device driver in VMS (or other OSes) have different limits. There is 
no distinction between "data disks" and other disks. They are all just 
disks.

   Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol