I was kind of frustrated over this myself, constantly failing to get a working hdf file for use in A600GS.
Any new hdf I created gave me errors, like 'Not a DOS disk in drive HD0'
Older hdf's I had lying around did work, so I could reuse them, but being limited to one HDD only I wanted a bigger drive.
Turned out it was caused by the system I used in WinUAE to format the new drive that caused this. Both my Amikit and my old A4000 winuae setup are based on OS3.9 and after formatting the disk there simply didnt work even if I selcted FFS as the filesystem when formatting.
Setting up a WB3.1 environment in WinUAE and then I was able to format a 2 GB hdf file and now got it working in A600GS
