[CentOS] Need a Centos 6 USB hard drive recovery procedure

Sat Jun 1 16:00:06 UTC 2013
Rock <Rocksockdoc at gmail.com>

On Sat, 01 Jun 2013 12:25:01 +0200, Louis Lagendijk wrote:

>> Should I now format the 2TB disk using this command?
>>  $ sudo mkfs /dev/sdb1
> You could try without reformatting it: just check where it is mounted:
> mount |grep sdb1 

Hi Louis,

I'm ready for the big dd!

OK. Starting over after a reboot, given these two disks:
A. The 500MB USB disk is the "good" disk
B. The 150MB USB disk is the "bad" disk

I run these commands (documented to help others on Centos):
a. Open a wide window & type "sudo tail -f /var/log/messages"
b. Plug in the good disk & note where it mounted:
==> Jun  1 08:26:39 rock kernel: usb 1-1.2: 
==> new high speed USB device number 5 using ehci_hcd
==> Mounted /dev/sdb1 (Read-Write, label "SignatureMini", NTFS 3.1)
==> Cmdline options: rw,nosuid,nodev,uhelper=udisks,uid=503,gid=503,dmask=0077
==> Mount options: rw,nosuid,nodev,uhelper=udisks,allow_other,nonempty,atime,fsname=/dev/sdb1,blkdev,blksize=4096,default_permissions
c. $ mount | grep sdb1 
==> /dev/sdb1 on /media/SignatureMini type fuseblk (rw,nosuid,nodev,allow_other,blksize=4096,default_permissions)
$ sudo mount /dev/sdb1 /mnt
==> Mount is denied because the NTFS volume is already exclusively opened.
==> The volume may be already mounted, or another software may use it which
==> could be identified for example by the help of the 'fuser' command.
$ sudo umount /dev/sdb1
$ mount | grep sdb1 
==> reports nothing
$ sudo mount /dev/sdb1 /mnt
==> reports nothing (but no errors either)
$ mount | grep sdb1 
==> /dev/sdb1 on /mnt type fuseblk (rw,allow_other,blksize=4096)
Here is where I had to reboot a moment ago ... but we can pick up from 
here now that I've repeated the commands without errors.
>> 3) I assume here that your bad disk is already connected (as sdz check
>> first what the real name is)

OK. Now I connect the bad disk & check /var/log/messages:
==> Jun  1 08:34:26 rock kernel: usb 3-2: new high speed USB device number 2 using xhci_hcd
==> Mounted /dev/sdc1 (Read-Write, label "SignatureMini", NTFS 3.1)
==> Cmdline options: rw,nosuid,nodev,uhelper=udisks,uid=503,gid=503,dmask=0077
==> Mount options: rw,nosuid,nodev,uhelper=udisks,allow_other,nonempty,atime,fsname=/dev/sdc1,blkdev,blksize=4096,default_permissions

Doublechecking how the bad disk is mounted:
$ mount | grep sdc1
==> /dev/sdc1 on /media/SignatureMini type fuseblk 
==>  (rw,nosuid,nodev,allow_other,blksize=4096,default_permissions)

> mount |grep sdc1
> and umount it to be sure

OK. I will umount the bad disk:
$ sudo umount /dev/sdc1

And, I check that the bad disk is unmounted:
$ mount | grep sdc1
==> reports nothing
>> dd if=/dev/sdz of=/mnt/image.dd bs=1M
>> This will copy the contents of your bad disk to image.dd
> this now becomes:
> dd if=/dev/sdc1 of=<path to the mount point for the new disk/image.dd

OK. This is where we don't want to make a mistake!
Q: Does the block size matter?

$ dd if=/dev/sdc1 of=/mnt/image.dd 

When that finishes, I'll run:
$ sudo chmod uog=r /mnt/image.dd

And, then the recommended testdisk recovery steps.

Wish me luck as I'm running the DD as soon as I send this
(I was confused which block size you recommended, as you
initially had 1M and then didn't have any size).

NOTE: The detail will be put into a tutorial for Centos users
which will have all the "idealized" steps, in sequence; so
your kind efforts not only help me, but many others (we hope).