Delta disk images?

[KillaByte]

Hi,

I've seen a very neat feature regarding disk images on the QEMU full system emulator lately (more precisely: on the qcow2 disk image format): delta images.

In short this means that you put a disk image on top of another already existing image which stores only the changes made. This can be implemented rather efficiently using copy-on-write.

I think that this could be quite useful in WinUAE, too. That way you could create a base HDF image containing a vanilla OS 3.9 install and create delta-HDFs for various purposes based on that base image.

It could also be a nice solution for write protected disks where you could store the changes in a delta-ADF and keep the original images clean.

Or you could plug in a real Amiga HD in RDB mode and layer a delta image on top of that.

Sure - you could always keep a safe copy of the original image around and replace the image with the good copy if you messed something up but I think delta images are a much more elegant solution.

While the qcow2-like solution operates at a very low level and would therefore also be usable for NDOS disks, a solution operating at file level like UnionFS (as used on the KNOPPIX Linux LiveCD) would also be thinkable. That way I could install an application and have all the files the install modified on the base image in a separate image to examine and archive.

[Toni Wilen]

ADFs already support this transparently (if original adf is unwritable = inside archive or image type without write support) Note that it is not possible to change path or filename, it always goes to "saveimages".

Hardfile images: will be supported someday. Most likely will use growing dynamic VHD images.

[KillaByte]

Neat!

[andreas]

Neat? Hmmm...well sometimes this even turns out to get awkward.
Supposed I forgot to unzip my ADF and just use it as a ZIP file.

Now I uncheck "write protect" and e. g. hand-edit some blocks in the disk with a disk editor.
The fact that WinUAE creates delta save images did not become clear until I tried using the saveimage as an ADF in WinUAE after warm reset, and nothing worked

Currently I have not found any possibility yet to have ALL data (incl. the modified) permanently written back to an 880K non-delta image, unless I go using some disk copying tool inside emulation, copying it to a blank floppy
Somewhat cumbersome...so I just remember now to unzip my zipped ADFs when I do this kind of work. For if I forget it, I can start all over again with my edits from the beginning...