integritysetup: Work without formatting entire disk (and/or format disk faster or partially)

At the moment running integritysetup format /dev/sda (where sda is an 8TB WD Red) results in initiation of a process estimated to take 3300 minutes, as the format is only able to sustain 40MB/s of throughput.

This isn't the most fun to watch so I have a few ideas on how to deal with it:

• Add a feature for wiping only partial segments of the disk (a workaround for the above).
• Add a "recovery mode" that ignores errors but also allows writes so that the disk can be initialized (for example by luksFormat or mdadm, which like to read things that aren't ready yet).
• Optimise the format to run faster. Read/write bigger blocks perhaps? I'm not sure why exactly it's so slow in the first place. blktrace doesn't show anything that looks obviously wrong to me.