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<div class="moz-cite-prefix">On 09/12/2015 03:21 PM, Mike Miller
wrote:<br>
</div>
<blockquote cite="mid:alpine.DEB.2.02.1509121512510.11939@taxa1"
type="cite">Wow, Dan, thanks so much for all the ideas! This is a
huge help. Here's what's going on:
<br>
<br>
I already formatted the new drive with ext4 and copied 3 TB of
data onto it, so I don't want to undo all that right away, but
there is another, probably more appealing way to go:
<br>
<br>
/dev/sda and /dev/sdb are identical 2 TB drives that were
previously in a RAID1. It looks like sdb somehow disconnected
from the RAID, but sda kept working for a few months before it
failed. I can mount /dev/sdb1 just fine and I copied all the
files off of it onto the new external drive. I had no errors. So
maybe /dev/sdb is in pretty good shape. Now that it's backed up,
maybe the best plan is to try to copy /dev/sda to /dev/sdb using
one of the dd tools.
<br>
<br>
So here's a question: /dev/sdb is formatted for ext4. If I want
to use it as the destination drive for the dd copy, do I have to
use parted to remove the partition table first? Or what?
<br>
<br>
Thanks again!
<br>
<br>
Mike
<br>
<br>
</blockquote>
<br>
You don't have to worry about the partition tables or anything -
because rather than copying a partition - such as /dev/sda<b>0</b>
you will just be copying the entire disk - so /dev/sda. <br>
<br>
When you copy the old (failing) disk onto the other disk (that is
either the same size, or larger) you will be copying _everything_ -
including the partition table, and the formatting info of the file
system. The contents of the disk you are writing to will be
completely overwritten.<br>
<br>
So then your replacement disk will be (exactly) what the failing
disk was, partition table, labels, filesystem and all. Though, you
will likely have some subtle corruption where blocks that couldn't
be read have the wrong bit value. <br>
<br>
So, if you do manage to recover some things - keep in mind that some
of the files my have subtle corruption. <br>
<br>
Will you notice if 8 bits are flipped in a 2 GB movie? Probably
not... but you would really just have to test the more important
files that you recover to make sure they aren't worse than your
several month old backup.<br>
<br>
Dan<br>
<br>
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