This thread really is about anything isn't it?
Well, you're the OP..... maybe you can append to the title and also say "and optimisations" or something after the SOLVED part.
Regarding the Mask, I do not know specifically if OS4 behaves differently to OS3.9, as I have not needed to change the Mask value for any hard disk partitions.
But if you set the Mask to 0x7FFFFFFF - then all of the first 2GB of memory can be used. The last character being F means the driver/controller is not fussy about memory alignment. The last letter could also be set to E or C for different alignments. For those drivers (e.g. in OS3.9) that may only operate in 24-bit memory space (i.e. first 16 MB) you can set the mask to 0xFFFFFF - I needed to do this once for a CD driver in OS3.9 that would have random errors otherwise.
There is an *excellent* explanation in the old SFS 1.58 guide (from original SFS author archive or SFS_OLD.guide in latest 68k full sfs1.277 archive) under the section "the Mask field":http://www.amiga-stuff.com/text/filesys ... S158.guide
I do not know which one is ultimately preferred out of 0XFFFFFFFF (4GB) or 0x7FFFFFFF (2GB), both for current systems, and for future compatibility.