Re: [Bug-ddrescue] GNU ddrescue suggestion - access to unaccessable Hard Disk

[Sam]

Al,

Regarding your earlier message today about strange characters in filenames, I 
completely agree with the earlier reply from Matthew (MMR).  In short: The 
behaviour you describe is not related to, nor caused by, ddrescue, and so 
cannot be and should not attempt to be, fixed by ddrescue.  As he said, when 
using ddrescue to clone a partition into an image file (as you described), 
ddrescue has no knowledge about, and does not attempt to interpret, the 
filesystem on that partition (if any).

Regarding your second message (below), again, you're misunderstanding the 
capabilities of ddrescue, given the Linux APIs that it has available for use, 
and the way that disk drives work internally.  I'll try to answer your 
questions:

> [...] it might be possible that the problem is that the

> hard disk has failed in the areas where it stores the
> information that it reports to the PC's Bios.

That area of the disk is typically called the SA (System Area) and is not 
accessible via standard commands.  DR companies use (expensive) software bought 
from the limited number of places who have reverse engineered such commands, in 
order to access the SA on disks.  Understanding what SA problem exists, and how 
to fix it, requires a detailed understanding of proprietary information.  You 
also have to consider that what appears to be a problem with the SA, can have 
many different potential causes, each of which needs a different solution (some 
requiring cleanroom intervention).  For example, your disk may have a hardware 
problem that prevents the SA from being readable - and not a problem with the 
SA itself at all.


> I found the following comment on a website;
>
> "I cannot imagine anything that could recover data from a
> /dev that isn't there."
> ref:

> http://forum.cgsecurity.org/phpBB3/dev-disappears-using-dd-rescue-t1183.html
>
> Is this comment totally correct?

For normal users, without access to the skills and investment of DR companies 
in both education and tools, and assuming the disk is not one of the very few 
where a well-known problem and solution exist, then for normal Linux software: 
Yes.


Occasionally some information is leaked about how to access disk firmware on 
specific disks, but that does not mean that there is a step-by-step tutorial 
about how to fix each individual type of problem.  Therefore the chances of 
success without you making a huge investment in time and research means that, 
again, the answer to your question is, realistically: Yes.

Your only realistic choice (unless you have plenty of patience and are willing 
to take risks that may destroy your data beyond recovery) would be to contact a 
suitably experienced DR company.


> Q1) is it possible to either include information on how to
> access the hard disk, then use dd_rescue?

That's not a reasonable expectation for disks with the behaviour you described, 
as I explain above.

> Q2) is it possible to have some features in dd_rescue that

> could attempt to access a device attached to a port or group
> of ports on a PC, and maybe extract the data somehow?

Assuming that you are still talking about a disk which is not recognised by 
Linux, then again, it's not a reasonable expectation for ddrescue to "somehow" 
achieve that as a generic feature.

Regards,

Sam