Chris

The “dd” tool is a very useful tool in Linux, it can be used to backup your entire hard disk or just parts of it. It is important to know that if you backup your full hard drive, the destination drive must have exactly the same, or more disk space than the source drive.

I use it to make a full backup of my servers root partition every week.

Some examples:

This will create a backup of your entire hard disk (hda) and will output a compressed image file.

dd if=/dev/hda | gzip > /path/to/image.gz

Create a backup of partition hda1

dd if=/dev/hda1 | gzip > /path/to/image.gz

This will restore the image to “/dev/hda”

dd if=/path/to/image.gz of=/dev/hda

Backup the Master Boot Record

dd if=/dev/hda of=/path/to/image count=1 bs=512

Restore Master Boot Record

dd if=/path/to/image of=/dev/hda count=1 bs=446

I have a server installed with Linux distribution Centos 4, I recently replaced the main harddrive and because the new drive was quite bigger (160gb vs 80gb), and I did not want to do a fresh install, it was needed to extend the root (/) partition. I used “Clonezilla” to backup and restore the data from the disk. After restore on the new disk I had about 74 GB of unused diskspace, so I wanted to merge it with the root partition.

Because the partition is LVM, and it is not readable by most partition/GUI tools (like gparted), it has to be done in another way.

Note. Fedora comes with a GUI LVM tool (system-config-lvm) , we do it via console.

1. Put the Linux Rescue cd-rom in the cd-rom drive and boot.
2. Open a terminal and type: pvdisplay

It will show something like this:

 --- Physical volume ---
  PV Name               /dev/hda1
  VG Name               VolGroup00
  PV Size               1.44 GB / not usable 0
  Allocatable           yes
  PE Size (KByte)       32768
  Total PE              46
  Free PE               1
  Allocated PE          45
  PV UUID               auQ2kD-GuHQ-6feE-nSr9-cA0A-dGbD-CrHZhg

 Here you can see the details (size etc.) of the Physical volume, now we need to add space to this volume (VolGroup00)

3. Open “gparted” and create a new partition from the unallocated space (ext3 recommended)
Notice the name of the new parition (i.e hda2)

4.  Open the terminal and type: pvcreate /dev/hda2

[root@localhost ~]# pvcreate /dev/hda2
  Physical volume "/dev/hdb" successfully created

5.  Type pvdisplay

[root@localhost ~]# pvdisplay
  --- Physical volume ---
  PV Name               /dev/hda1
  VG Name               VolGroup00
  PV Size               1.44 GB / not usable 0
  Allocatable           yes
  PE Size (KByte)       32768
  Total PE              46
  Free PE               1
  Allocated PE          45
  PV UUID               auQ2kD-GuHQ-6feE-nSr9-cA0A-dGbD-CrHZhg
 
  --- Physical volume ---
  PV Name               /dev/hda2
  VG Name               VolGroup00
  PV Size               3.97 GB / not usable 0
  Allocatable           yes
  PE Size (KByte)       32768
  Total PE              127
  Free PE               127
  Allocated PE          0
  PV UUID               6TvkYu-sY2K-tIsj-aXZh-KLPb-81Ox-oPIFyO

Now we need to merge the newly created partition into one volume group.

6. Extend the current volume group with the new partition:

[root@localhost ~]# vgextend VolGroup00 /dev/hda2
  Volume group "VolGroup00" successfully extended

7. Remember the space of the new partition, so we can add this to the current Volume Group (/dev/hda1)

[root@localhost ~]#  lvextend -L+3.97G /dev/VolGroup00/LogVol00
 
Rounding up size to full physical extent 5.31 GB
Extending logical volume LogVol00 to 5.31 GB
  Logical volume LogVol00 successfully resized

8. Bootup Linux and resize the volume to the actual size

[root@localhost ~]# ext2online /dev/VolGroup00/LogVol00

You can check the new size with “df”