Hard Drive Data Recovery

November 13th, 2014

This article discusses hard disk data recovery on Linux using dd and fdisk.

I recently left for a trip to South America, and took my trusty Intenso 320GB external drive with. Well aware that I’ve dropped it a couple too many times and that it was beginning to click more and more often during regular usage, I took a full backup before leaving. There’s nothing critical on the drive that I don’t have additional copies of elsewhere, however losing it would be a pain.

Having reached Madrid airport, I plugged the drive in and was about to pull some documents off it when disaster struck. The drive just clicked for about 30 seconds before Windows prompted me to format it. I tried removing it and reinserting it a couple of times but no luck – the drive had failed. I went to the duty free store in the airport and picked up a 1Tb WD Elements drive for 99 Euros, and planned to attempt data recovery when I arrived in South America.

I’m keen to get the data recovery started – it’s going to take a while on my USB 2.0 laptop and the more bad sectors, the longer it will take.

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Move Xen Guest from loopback filesystem to LVM

October 25th, 2009

Moving a Xen Guest into an LVM container from a loopback sparse image is easy enough.

You’ll need to power down the VM using xm shutdown mymachine

Once done, create the logical volume with: lvcreate –name mymachine-disk –size 10G myvg 10G should match the exact size (if not more) of your current VM. Now create the same for the swap file: lvcreate -name mymachine-swap -size 128M myvg. Now edit your machine’s config (/etc/xen/mymachine.cfg), replacing the disk part from:

disk        = [
‘file:/xen/mymachine/mymachine-swap,sda1,w’,
‘file:/xen/mymachine/mymachine-disk,sda2,w’,
]

to

disk        = [
‘phy:/dev/myvg/mymachine-swap,sda1,w’,
‘phy:/dev/myvg/mymachine-disk,sda2,w’,
]

And use dd to write the disk to your new LVM filesystem:

dd if=/xen/mymachine/mymachine-disk of=/dev/myvg/mymachine-disk
dd if=/xen/mymachine/mymachine-swap of=/dev/myvg/mymachine-swap

Remembering that you can use killall -SIGUSR1 dd at any time to gain a status update on dd’s IO.

Once done, power up your VM again with xm create mymachine.cfg

Setting up an LVM filesystem

October 20th, 2009

Setting up an LVM filesystem is quite easy assuming you have the right tools installed and a recent kernel. LVM has a lot of advantages, most notably the ability to take snapshots of the current filesystem – this is why LVM is often used in live database environments.

Assuming a Debian Lenny machine, get the relevant packages. Some may already be installed:  apt-get install lvm2 dmsetup mdadm

In this example, we will assuming that /dev/sda is your boot drive, and that you want to leave it out of your LVM array, but include /dev/sdb and /dev/sdc. Both /dev/sdb and /dev/sdc should be of equal sizes.

Firstly, using fdisk, remove any existing partitions with ‘d’, on /dev/sdb and /dev/sdc, and create one new partition to span the drive. Change the partition type to ‘8e’ which is the LVM type.

Now prepare your physical disk for LVM with the ‘pvcreate’ tool:

pvcreate /dev/sdb1 /dev/sdc1

Note that you can reverse this with pvremove. You can also use pvdisplay now to display information on all physical volumes.

Oh – you do realie that you can use /dev/mdX just as easily to create LVM on your RAID devices?

Now, we need to create a ‘volume group’: vgcreate myvg /dev/sdb1 /dev/sdc1

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dd progress update

October 14th, 2009

While a long `dd’ is running, how can you get a progress update?

kill -USR1 `pidof dd`

This will send the SIGUSR1 signal to dd, which according to it’s man page causes it print it’s progress to STDERR. Useful to know..

APNIC Box – Linux on a Mikrotik 532a, Part 3 – Installing Debian, Prebuilt Disk Image

October 5th, 2008

Follow on from 01 Oct 08 APNIC Box – Linux on a Mikrotik 532a, Part 2

The device runs a 2.4.30 kernel on a debian woody (mipsel) environment. If anyone can contribute anything for 2.6.x and debian etch, that would be great.

Installation instructions:

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