With dd (coreutils) the sparse operator works.
The background of that procedure is to have an image that can be used in virtualbox. I'm not sure if virtualbox is able to handle a gz file..?
How do you mean this: dd isn't mounting the correct filesystem? The problem isn't limited to dd, the othr programs I tried ended up in the same.
As far as I could see in the meanwhile, it's actually due to the file size restriction in fat 32 that I cannot get the whole partition content into one big file. So obviously I now have the two possibilities:
1. I tell dd / ddrescue / partimage to split the image into several smaller files (but then I would get the problem how to merge them on that fat 32 hdd into a fil that is bigger than 4.3 GB, so this isn't a real possibility
2. I get it handled that virtualbox can process a compressed gz img file.
I wonder how others have accomplished the same issue: creating a partition image and loading into a VM - I can't imagine that this issue is a rare case. Perhaps it's just because they're not using a fat 32 formatted hdd..