I downloaded something that came as three large files: One was a
*.dmg (a disk image file, which I expected) and two more were
*.dmgpart files, which I haven't happened to see before – I never downloaded something so large on my Mac!
I suppose these *.dmgpart files are just the parts of a single disk image, but spanning three files so each can fit within a target size for media backup purposes. For instance, the first two parts of my download were 4.3GB each, conspicuously the capacity of a single-layer DVD-ROM.
Is my supposition about
*.dmgpartfiles correct, or did I miss something key?
How long ago were these multi-part disk image files introduced in Mac OS X?
Is there a logical limitation to the
*.dmgfile format itself requiring images over a certain size to be made multi-part, or is it an optional facility for spanning media only?
How can I create multi-part disk images like this? Is this supported by the standard tools (i.e. Disk Utility), or are special command-line or other tools required?
Is there an easy way to merge the parts back into a single disk image? (One could conceive making the mistake of not copying an entire set – not a problem where only a single image file is involved.)
Is there an easy way to split an existing very large disk image into a spanned set?