Work on adding write ability to the filesystem is progressing nicely, but I was momentarily disconcerted by a little detail of SimNow. By default, all disk writes are journalled; this means that, unless you disable this feature or manually commit changes, changes won’t be saved to the disk image. I wondered why my disk writing routines seemed to be working when looked at under the debugger but weren’t saving anything permanently to the disk! Have a look at the manual to find details of this feature (which I can see is actually very useful when you are experimenting).
By the way, there’s a new version of SimNow out that allows you to add and delete devices from the virtual machine that you are using. It also seems slightly faster to me, but that could well be a combination of my imagination and changes that I have made to IanOS.