As far as I can see, comparing dd with ddrescue can be concluded saying that ddrescue is far better at rescuing data from broken data sources. dd does not have this ability.
Sometimes I simply don't now if a data source is completely fine or if it is broken in some way before starting the backup.
So why not forget about dd and simply use ddrescue every time?
Isn't it like this: If the data source is fine ddrescue will do a fine backup and if the data source is broken ddrescue may be able to handle this.
The only reason I can see so far would be if dd is available and ddrescue is not, but I think in most cases when someone is doing a backup he can probably gain root access and simply install ddrescue.
Does ddrescue operate in any way slower than dd on fine data sources?
Best Answer
Quite simply? DD is a standard tool which you will predictably find in some shape or form in most unix or unix inspired OS. Its designed around being minimal and simple. That's its only advantage. There's no built in verification, there's no check summing, there's no fancy bits. However you can walk to any linux system and do an image. Its a hammer. Its a bit of steel on a stick, you know every workshop has one, and it bashes in nails fine. And at the very least it looks something like this, and any other hammer you find does at least what this does. ddrescue also should give you a bit-perfect copy you can verify with a checksum.
It drives in nails and it takes them out. It gives you the best chance of recovering data but at the cost of possibly more time, and the optimisation being for maximum data recovery over perfectness. It also would do an image of a drive that's perfectly healthy.
I also personally favour the gnuddrescue syntax. Its simpler and more idiot proof in my opinion.
I'd add a PROPERLY done image with any of these tools would essentially be usable in the same way.
Most unix greybeards would say "Use the big bashy thing" - its the "right" way to do it. I prefer gnuddrescue since its just a more elegant tool for the end user, that happens to do more. That said, in some cases knowing how to use both can be useful, for example when dealing with a system where you can't install what you prefer.