Date   : Tue, 22 Aug 2006 11:18:04 +0100
From   : "David Harper" <dl.harper@...>
Subject: Re: Hard disk backup - another challenge

Andrew Benham wrote:

> ...
> Anyway, part way through transferring 17.5 MegaBytes of data, I
> looked at the file accumulating on the more modern machine, and
> was surprised to see the program was transferring loads of
> sequential 'blank' sectors.  The disk was fully *COMPACTed before
> I started, and I stop transferring when I hit the start of the free
> space at the end of the drive map.  So all the sectors being
> transferred should be 'active' ones.
>
> Ah, that'll be the 10 MegaByte $.DOS.DRIVE_C file then - i.e. the
> file used by the 80186 Co-Processor to provide the DOS+ file system.
> That DOS+ file system is nothing like full, so there's loads of
> sectors which I don't need to backup.
>
> Looks like my backup program needs to not only understand the ADFS
> free space, but also the free space in the $.DOS.DRIVE_C file too...

ADFS sees the whole of $.DOS.DRIVE_C as a single file and has no way of 
understanding its contents. A simple ADFS back-up is bound to transfer the 
whole of this big "file" entire.

If you are just going to transfer the data that forms part of true files, 
then your program is going to have to treat the DOS+ partition file as a 
special case, and will need to be able to interpret the FAT within it.

I somehow doubt that you will find a program to do this, unless you are 
willing to write it yourself, and that would be a major task.

David Harper