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Re: Help with ddrescue

On 05/08/2015 at 07:33 PM, German wrote:

> On Fri, 08 May 2015 19:20:37 -0400
> The Wanderer <wanderer@fastmail.fm> wrote:
>> On 05/08/2015 at 07:08 PM, German wrote:

>>> That's what I got:
>>> spore@asterius:~$ lsblk
>>> sda      8:0    0 119.2G  0 disk 
>>> ├─sda1   8:1    0   512M  0 part /boot/efi
>>> ├─sda2   8:2    0 111.3G  0 part /
>>> └─sda3   8:3    0   7.4G  0 part [SWAP]
>>> sdb      8:16   0 465.8G  0 disk 
>>> sdc      8:32   0   1.8T  0 disk /media/spore/9F86-0131
>>> sdd      8:48   0   1.8T  0 disk 
>>> └─sdd1   8:49   0   1.8T  0 part 
>>> Where sdd is my failed drive. sdc is my spare drive. The correct
>>> procedure will be ddrescue if=/dev/sdd1 of=/dev/sdc ?
>> No. That might potentially work (except that, if I'm reading the
>> ddrescue man page correctly, the syntax is wrong), but it wouldn't be
>> correct.
>> First, unmount /dev/sdc.

Note for the record: The other steps will erase any data which is
presently on /dev/sdc. I figure you probably already know that, but I
just want to be explicit about it.

>> Then do one of two things:
>> 1) Create /dev/sdc1 (as an unformatted partition, using fdisk or
>> parted or whatever partitioning tool you choose), and then run
>> ddrescue /dev/sdd1 /dev/sdc1 /any/path/you/want/ddrescue.log
>> 2) run
>> ddrescue /dev/sdd /dev/sdc /any/path/you/want/ddrescue.log
> Ok, I think I am getting closer. How big is a log file?

The size of the log file depends on two things: the size of the data
source which is being copied/rescued, and the number of errors which
occur while attempting to read that data source.

It can be very small, or it can be moderately large. Even in a
ridiculous case, however, I wouldn't expect it to be more than a few
hundred megs - unless the source drive is so bad that you're not going
to be getting any data back off of it anyway.

> Can it be anywhere on all drives that have enough space? For
> instance:
> ddrescue /dev/sdd /dev/sdc /dev/sda2/ddrescue.log will work?

Not quite. /dev/sda2/ is not a directory; it's a device node.

Since /dev/sda2 is mounted to / (the root filesystem), the correct
equivalent to this command would be:

ddrescue /dev/sdd /dev/sdc /ddrescue.log

and although I wouldn't advise storing a log file in the root directory,
the command should work.

The log file itself can be placed in any writable location which has
enough space.

   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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