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Re: Help with ddrescue

On 05/08/2015 at 02:48 PM, Gary Dale wrote:

> On 08/05/15 02:32 PM, German wrote:
>> On Fri, 08 May 2015 14:23:39 -0400 The Wanderer
>> <wanderer@fastmail.fm> wrote:

>>> Yes, that's what I'd do in your situation. A 2.5TB drive should
>>> be more than enough; that would also let you store the 
>>> sdb_failed.ddrescuelog file on the same drive, if you need to, so
>>> you don't have to worry about finding space for it elsewhere.

>> Thanks so much. I wait when I can get a bigger drive. Have a
>> greatest day!
> I think Wanderer may be overstating the problem a little. If the two
>  drives are exactly the same size, you can use ddrescue to duplicate
> the failed drive onto the new drive (ddrescue if=/dev/sdb
> of=/dev/sdc). However this will limit you to recovering in place on
> new drive.

In my experience, single-pass recovery like this does not work very
reliably or very well; it also doesn't let you make the "backup copy"
you originally suggested, which is a good idea if you have the space
(though I never have had).

It's technically possible, yes, but I wouldn't want to trust or rely on
it in any case where the source device is potentially prone to failure -
and in any scenario where it isn't, you're unlikely to want to use one
of the *rescue tools in the first place.

(There's also the consideration of finding space for the ddrescue log
file if you're restoring directly to the identical-size device; that
file that may not be as important in some scenarios, but I wouldn't want
to try to do such a rescue without one.)

> Hopefully the file system is repairable which will make this
> possible. If the file system isn't, you need a third drive to hold
> recovered files.

That's another point, yes; if the filesystem isn't directly repairable,
you may have to use forensic tools to dig in and recover data, and at
that point it's just easier to work with a separate file IMO.

I certainly wouldn't say there are never times when direct
device-to-device recovery like that is appropriate, but I haven't
encountered one and I would not recommend it as a base-practices

   The Wanderer

The reasonable man adapts himself to the world; the unreasonable one
persists in trying to adapt the world to himself. Therefore all
progress depends on the unreasonable man.         -- George Bernard Shaw

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