Re: [Bug-ddrescue] user-interface suggestions

[Richard Neill]

Antonio Diaz Diaz wrote:
> Richard Neill wrote:
> > Here lies the problem. It's going to be hard (I think) to write a 
> > suitable heuristic for ddrescue.
>
> The problem is that, AFAIK, there is no way for ddrescue to know the 
> block size of a device except by means of user-supplied arguments.

So, how does the user know this? If I sit down at a Linux machine, which 
has some item of dodgy hardware (probably a regular SATA disk, but maybe 
 PATA, maybe a floppy, maybe a RAID array, or maybe even a USB-disk or 
a  CD-ROM), how am I supposed to find out the block size?

Is this a property of the underlying hardware, of the linux device 
driver, or of the filesystem?

Googling for this has multiple answers, stating authoritatively that the 
BS is one of  512, 1k, 2k, 4k or 16k. The only thing I've learned is 
that "block size" can mean more than one thing.

> > Is there any way to simplify the heuristic such that ddrescue can make 
> > its own decisions about what is "nearly" the best outcome? It doesn't 
> > have to be spot on. But at the least, ddrescue should protect the user 
> > from any bad consequences of the misuse of -d.
>
> There aren't such bad consequences. If the values supplied are correct, 
> ddrescue will rescue data. If not, all reads will fail fast, but you can 
> stop it and try other values.

Is that obvious to the user? Is it clear from the error message that the 
error is due to the wrong blocksize specification, and not just because 
the disk itself is failing? (After all, the user probably *expects* 
reads to fail because the hardware is broken).

Best wishes,

Richard