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Re: [linux-lvm] Rebuilding ext4 filesystem on an LV

On Thu, Jul 8, 2010 at 12:13 PM, Stuart D. Gathman <stuart bmsi com> wrote:
On Thu, 8 Jul 2010, Stuart D. Gathman wrote:

> Method 2:
> With both new and failed drive connected, use dd_rescue or equivalent to
> copy (most/some of) the failed drive to the new drive.  Remove failed
> drive and bring up VG.  If UUID was not readable on failed drive, use
> pvcreate to restore it on new drive.

(Question: does new drive need to be same physical size? can Or can I just create a new partition with the old size - new drive is bigger.)

The real problem seems to be that the LV appears to the LVM as not formatted. I am guessing this is because not only the partition got trashed, but also the superblock(s)  data. I have tried to find backup superblocks, but I keep getting the ioctl error, even from mke2fs. I will try dd_rescue - I have to install it, since it is not by default.

I added a new drive to the LV, and tried pvmove, but, I got the ioctl error again with that.

I should mention that an external case-free USB adapter is the best way
to attempt recovery of failed drives.  You can even run the IDE/SATA/Power
cable to a box in the freezer (and the USB adapter can sit on top of the
freezer and a long USB cable go to your computer) - which often helps recover
data from failing drives.

If the mountain won't come to Mohammed... I can always just get a large bag of ice and (carefully wrapped up in waterproof cover) put the drive into it. Will try that also :-).

FWIW: I did run dmsetup _table, and from /var/log/messages:

Jul 12 09:17:25 Elmer kernel: device-mapper: ioctl: error adding target to table
Jul 12 09:24:16 Elmer kernel: device-mapper: table: device 253:3 too small for target

Couple of thoughts:
* Using dd_rescue, is there a utility that can read through the physical blocks on the drive, searching for something that looks like a superblock?

* Or, is it possible to physically disconnect the bad drive, bring up the remainder of the LV with the hope of recovering whatever data was on those drives. Att this point, I am resigned to the fact that the first drive is dead or on its last gasp (SMARTD says something like: "Danger (Will Robinson!) drive failure imminent. Back up data immediately.)" But the other drives in the LV should have something on them still. Right?

As always thanks for the help.

             Stuart D. Gathman <stuart bmsi com>
   Business Management Systems Inc.  Phone: 703 591-0911 Fax: 703 591-6154
"Confutatis maledictis, flammis acribus addictis" - background song for
a Microsoft sponsored "Where do you want to go from here?" commercial.

"All consuming fires of hell" - very loose translation from Mozart's unfinished Mass for the Dead :-)


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