[Bug-ddrescue] Disk blocks

[David Morrison]

https://twocanoes.com/winclone-image-compatibility-with-512-and-4k-block/

I came across this article which describes some in-depth behaviour of 
disks, and how it has changed in 2015 and later Macs. The same may 
well apply to other operating systems. I wonder if this will affect 
how ddrescue operates?

Briefly, originally disks used 512 byte sectors. In recent years, 
disks have started using 4096 byte sectors. However, Mac operating 
systems using these disks still returned 512 byte sectors until 2015.

So for example, to write a 512 byte sector, it was necessary to read 
the 4096 byte sector, update the 512 bytes, then rewrite the whole 
4096 bytes.

If there is a bad spot in that 4096, presumably the read will fail 
every time a 512 byte sector is read or written. So if ddrescue tries 
to read each 512 byte sector, it will be hitting that bad spot eight 
times. Apart from wear on the failing mechanism, it will presumably 
take eight times as long. :-(

Now the challenge might be to work out what the physical sector size 
of the disk is when it is being disguised by the operating system.

Cheers

David