RL02-USB Controller Status/Problem
bqt at update.uu.se
Tue Apr 7 14:25:07 CDT 2015
On 2015-04-07 20:54, Pete Turnbull wrote:
> On 07/04/2015 19:26, Johnny Billquist wrote:
>>> Well, yes, it's still bad, and still there, but all the RT-11 utilities
>>> use the substitute block.
>> So COPY/DEV is essentially only usable for opying RT-11 disks on RT-11
>> systems. :-)
>> Nothing wrong with that, mind you.
> Well, no, actually; I've been using it (under RT-11 V5.7) to copy other
> OS disks (mainly 7th Edition Unix) because it does that perfectly well
> :-) When the DL.SYS driver sees a disk changed, it reads the
> manufacturing defect list so it's still good to copy most disks.
But since the 7th edition Unix most likely do not treat the bad blocks
the same way as RT-11 does (skipping bad blocks), that means blocks will
get renumbered, and 7th edition will end up with a very corrupt and
broken file system.
Essentially, this will only work well if you don't have any bad blocks
on the device.
Just because you have a manufacturer bad block list on the disk, that
does not mean that different OSes handle the disk the same way.
Let me give you a very silly example.
Let's say we have a file system where each disk block points to the next
disk block in a file, and that the OS address each disk block in an
absolute manner. Bad blocks do not affect the block numbering.
Let's then say that we have the following 5 blocks:
Block # Content
n+2: <bad block>
n+4: 0 (EOF)
Now, if RT treats this as skipping over the bad blocks, it would skip
n+2, while n+3 would on the target device become n+2. However, block n+1
still points to n+3, so now we skip over one block of the file. Which
means we corrupted the disk.
I could create a whole bunch of similar scenarios, but I'm sure you can
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