[Simh] porting RL01 images to RL02

[Johnny Billquist]

On 2017-02-05 19:21, Paul Koning wrote:
>
>> On Feb 5, 2017, at 7:55 AM, Johnny Billquist <bqt at softjar.se> wrote:
>>
>> I'm not entirely clear about what you mean by "porting".
>>
>> Are you talking about getting the files and file system across from one type of device to another? If so, it might depend on the file system in question, but for the ones I can think of, in general, you can just copy the content to a larger device and it works just fine. You will not get access to the extra space though, as the existing file system only knows about the blocks that existed when it was created.
>
> For RSTS, that's often not true, for two reasons.  One is the "cluster size".  There's the device cluster size and the pack cluster size.  The former is the power of two such that device size in blocks divided by that cluster size is <= 65536.  The pack cluster size is the file system allocation unit.  It must be >= the device cluster size.  If you put a small device file system on a larger device, it may have too small a pack cluster size.
>
> The other, more limiting, issue is that the free cluster bitmap (file [0,1]satt.sys) must be large enough for the device the file system sits on.  If the pack cluster size still works for the device in question (for RL01 vs. RL02 that would always be true) you may well have a bitmap file that's too short for the larger device.
>
> Both of these issues will cause the OS to complain when you try to mount the file system.

Paul, I don't know much about the internals of RSTS/E (as you might 
know). Are RSTS/E going through these kind of checks on mount? In RSX, 
various kinds of parameters are stored in the FS home block, and what is 
used on all future mounts, and processing. These structures and data are 
just assumed to be inherently consistent, and no check is made against 
the actual disk drive, to check if the number of blocks on that device 
match against these structures.

The setting up of the values at file system initialization is taken from 
the device properties, and that is the only time when the relationship 
with the hardware is carried through.

And since some of these values are used for setting up various 
structures, it can be very hard to change the size of a file system 
after the fact in RSX, which is why I later on suggested that it's not 
something I would ever recommend anyone to try. But as long as you just 
live with the existing values, you will not have any problems with ODS-1 
at least.

	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