Did my backup fail?
 

I was trying to create a backup, SuperDuper got as far as creating a blah.dmg.sparseimage file but the failed trying to create a "read only" (whatever that part is) due to lack of space.

So I'm left with "blah.dmg.sparseimage" - is this a valid backup? Can I attach an external drive with more space then complete the operation with this file or do I have to repeat the whole process?

Thanks!

Why are you making a read-only backup? This is a legitimate read/write sparse images, yes...but we won't convert it if you run again.