Re: [Bug-ddrescue] Disk blocks

[Antonio Diaz Diaz]

David Morrison wrote:
> 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?

Ddrescue operates with byte positions, not sector numbers. Therefore 
sector size can't make ddrescue operate incorrectly, but an incorrect 
--sector-size may result in inefficient operation or even make direct 
mode refuse to work.


> 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.

If you find that all bad-sector areas in the mapfile have sizes multiple 
of 4096, most probably the sector size is 4096.


Best regards,
Antonio.