Source

Problem:

My computer only has 20GB of disk space. I just have 1 partition. I want to add another disk (40GB). I don’t want to add another partition (and I really don’t want to reinstall the whole system), I want to increase the size of the root partition to 60GB. i.e. I want the root partition to span across two physical disks.

Solution:

1. Add new physical disk. Boot.
2. # pvscan 

   This will show you the current physical volumes.

3. # fdisk /dev/sdb 

   Add the disk to your machine as a primary partition. Partition type: “8e (LVM)”. Obviously /dev/sdb may be different on your system.

4. # pvcreate /dev/sdb1 

   This creates a new physical LVM volume on our new disk.

5. # vgextend VolGroup00 /dev/sdb1 

   Add our new physical volume to the volume group: VolGroup00. Again, this group name may by different for you, but this is what Redhat & CentOS assigns by default when you install your system.

6. # pvscan 

   You should see the new physical volume assigned to VolGroup00.

7. # lvextend -L+40G /dev/VolGroup00/LogVol00 

   This increases the size of the logical volume our root partition resides in. Change the -L flag as appropriate.

We’ve just added 40GB to the logical volume used by the root partition. Sweet as. Now we need to resize the file system to utilize the additional space.

1. Reboot into rescue mode using your CentOS CDROM. 

   From memory this involves typing linux rescue as your boot option.

2. When prompted, skip the mounting of system partitions.
3. # lvm vgchange -a y 

   This command makes your LVM volumes accessible.

4. # e2fsck -f /dev/VolGroup00/LogVol00 

   Run a file system check, the -f flag seems necessary. No idea what we do if the returns an error?

5. # resize2fs /dev/VolGroup00/LogVol00 

   Without any parameters resize2fs will just increase the file system to the max space available.

Reboot and your root partition is now 40GB lager, spanning multiple disks.