Re: [Bug-ddrescue] Suggestion / feature request - bad head mapping

[Robert Trevellyan]

partclone is another tool that can create domain mapfiles for ddrescue,
potentially saving huge amounts of time on large, sparsely populated disks.
It isn't limited to NTFS (but it doesn't know anything about drive heads).

Robert Trevellyan

On Thu, Jan 4, 2018 at 5:47 PM, Scott Dwyer <address@hidden> wrote:

> I don't know of any tools that can create a domain file for targeting
> heads. It is too dynamic to be done in any easy way. Professional tools use
> special vendor specific commands to map heads. But I do know of a tool that
> can help target things in the NTFS filesystem.
>
> There is ddrutility, which can be found at http://sourceforge.net/project
> s/ddrutility/
>
> For the NTFS filesystem, it can create domain files for the MFT (file
> system table), and also the Bitmap (the used area of the disk). Someone
> recently posted in the ddrutility discussion area a very creative (but
> complicated) way of using the tools to actually create a domain file to
> target specific files.
>
> https://sourceforge.net/p/ddrutility/discussion/general/thread/e17d000c/
>
>
> On 1/4/2018 7:18 AM, Gábor STEFANIK wrote:
>
>> -----Original Message-----
>>> From: Bug-ddrescue [mailto:bug-ddrescue-
>>> address@hidden On Behalf Of Peter Clifton
>>> Sent: Thursday, January 4, 2018 12:02 PM
>>> To: address@hidden
>>> Subject: [Bug-ddrescue] Suggestion / feature request - bad head mapping
>>>
>>> Hi,
>>>
>>> I've been dumping a disk with ddrescue for a friend, and it occurred to
>>> me
>>> that one feature present in hardware based / proprietary recovery tools
>>> (as
>>> far as I could discern from watching youtube videos of professional
>>> recovery), is bad-head mapping.
>>>
>>> The pattern of slow / bad reads from this particular disk appears to be
>>> 75%
>>> good, 25% bad, in a fairly regular pattern. I know the disk has 2x
>>> platters, 4x
>>> heads, so this suggests (possibly), a damaged region of one platter
>>> face, or
>>> one read head wearing or damaged more significantly than the others.
>>>
>>> I was curious as to whether you had suggestion how (or interest in
>>> adding a
>>> feature), to have ddrescue focus on the 3/4 of the disk which is more
>>> readily
>>> accessible.
>>>
>>> I understand that LBA to head mapping can very quite significantly
>>> between
>>> different types of drive though, and I have no idea of the techniques
>>> used by
>>> the proprietary disk recovery tools to determine this mapping. (From the
>>> video I saw, it seemed to be read or determined by scanning the drive
>>> somehow.)
>>>
>>> Anyhow - also wanted to say thanks for the utility. An improvement over
>>> dd_rescue, and I'm sure it has saved many people much data. In this case,
>>> fortunately - the drive was _just_ accessible enough to pull the
>>> majority of
>>> the user files my friend wanted through the filesystem before starting
>>> the
>>> full disk image.
>>>
>>> I guess a related (but very advanced) feature one could imagine adding at
>>> some future point, is persuading ddrescue to focus on sectors of the disk
>>> which are identified as containing desired filesystem data (as
>>> proprietary
>>> tools do). Obviously this would require connecting with a filesystem
>>> driver,
>>> so would be rather a complex task. Is this kind of functionality on your
>>> wish-
>>> list for the future, or out of scope for ddrescue development?
>>>
>>>
>>> Kind regards,
>>>
>>> Peter
>>>
>> Hi,
>>
>> Domain mapfiles can be used for both purposes. You need a separate tool
>> to generate mapfiles containing the sectors accessible through each head.
>> Then, get the sector map of the desired files using another utility (in
>> mapfile format), and finally combine the mapfiles using the ddrescuelog
>> command.
>>
>> It would be probably best to automate this using some wrapper (with a GUI
>> or curses-based interface). It's definitely beyond the scope of ddrescue
>> itself.
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