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Re: Help with ddrescue

On 05/08/2015 at 02:16 PM, German wrote:

> On Fri, 08 May 2015 13:40:01 -0400 The Wanderer 
> <wanderer@fastmail.fm> wrote:
>> On 05/08/2015 at 01:20 PM, German wrote:

>>> Thanks, but some clarification is needed. Now I have two drives,
>>> failed and a spare. Both are 2TB in size. Failed drive probably
>>> has 1.6 TB data I'd like to recover. It has only one partition I
>>> suppose.
>> That's bad.
>> If the drive has only one partition, it probably has a single
>> filesystem taking up all of its space.
>> When you create a ddrescue image from that partition, the new image
>> will take up _at least as much_ space as the original filesystem.
>> That's not the 1.6TB of "used" space; it's the full 2TB of "total"
>> space. (Plus however much space is taken up by the "index" file
>> used by ddrescue while doing its work.)
>> That means that if your two 2TB drives are actually the same size,
>> the "good" one will not have enough space to store the image you
>> need to rescue from the "bad" one.
> Thanks Wanderer. So, I have no chances with two drives the same
> capacity? Would you advise to wait when I can get more capacity drive
> and only then to proceed as to save some head ache?

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.

> Once again, thanks for such a complete instructions.

I wouldn't call the directions I gave "complete"; there's a lot of
details you'll still have to work out on your own, because they will
depend on the exact details of your failure and the recovery process.
Still, they should at least provide you a good starting point.

Again, I would recommend that you install (and read the documentation
for) myrescue, and consider using that instead of ddrescue. I've used
both (as well as dd_rescue), but if memory serves I've had better
results with myrescue.

   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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