Re: [Bug-ddrescue] Trimming blocks even though set to read 1 sector at a time

[Antonio Diaz Diaz]

Hello Scott,

Scott D wrote:
> First I will say that this is happening with version 1.15, so if it is 
> different in the newer versions please let me know.
>
> I am using the option -c 1 to only read 1 sector at a time. The drive 
> has many bad single sectors (I think it got bumped hard during a write 
> and wrote across the disk in a spiral). So I don't want to read any bad 
> sectors twice as it doubles the read time and I know they will not read. 
> But even reading 1 sector at a time it still wants to trim the blocks 
> and performs another read of all bad sectors, which like I stated 
> doubles the read time. Is there a way to prevent this?

Ddrescue never reads a bad sector twice. (Unless given the -r option). 
The blocks ddrescue is trimming are the ones it first skipped.

Imagine you have a tiny disc with only 10 sectors. Ddrescue starts 
reading sector 1, then sector 2, but sector 3 gives an error. So 
ddrescue skips sectors 4 to 6 and goes directly to sector 7. It reads 
sectors 7, 8, 9 and 10 without errors finishing the copying pass.

Then ddrescue trims the block it skipped (sectors 4 to 6). It reads 
sector 6, then sector 5, and finally sector 4, which also gives an error.

As you can see, no sector was tried twice, and the remaining bad sector 
(4) was tried last.

Regards,
Antonio.