Add a new disk to a lvm2 partition (in ubuntu)

In my case i add partition /dev/hdc2 to lvm2 group
sudo su
pvscan
PV /dev/hda6 VG Ubuntu lvm2 [20.81 GB / 0 free]
PV /dev/hdc1 VG Ubuntu lvm2 [9.77 GB / 0 free]
Total: 2 [30.58 GB] / in use: 2 [30.58 GB] / in no VG: 0 [0 ]

fdisk /dev/hdc


Command (m for help): p

Disk /dev/hdc: 41.1 GB, 41110142976 bytes
255 heads, 63 sectors/track, 4998 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System
/dev/hdc1 * 1 1275 10241406 8e Linux LVM
/dev/hdc2 1276 4998 29904997+ 83 Linux

Command (m for help): t
Partition number (1-4): 2
Hex code (type L to list codes): 82
Changed system type of partition 2 to 82 (Linux swap / Solaris)

Command (m for help): t
Partition number (1-4): 2
Hex code (type L to list codes): 8e
Changed system type of partition 2 to 8e (Linux LVM)

Command (m for help): p

Disk /dev/hdc: 41.1 GB, 41110142976 bytes
255 heads, 63 sectors/track, 4998 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System
/dev/hdc1 * 1 1275 10241406 8e Linux LVM
/dev/hdc2 1276 4998 29904997+ 8e Linux LVM

pvcreate /dev/hdc2
Physical volume "/dev/hdc2" successfully created

pvscan
PV /dev/hda6 VG Ubuntu lvm2 [20.81 GB / 0 free]
PV /dev/hdc1 VG Ubuntu lvm2 [9.77 GB / 0 free]
PV /dev/hdc2 lvm2 [28.52 GB]
Total: 3 [59.10 GB] / in use: 2 [30.58 GB] / in no VG: 1 [28.52 GB]


vgextend Ubuntu /dev/hdc2
Volume group "Ubuntu" successfully extended


pvscan
PV /dev/hda6 VG Ubuntu lvm2 [20.81 GB / 0 free]
PV /dev/hdc1 VG Ubuntu lvm2 [9.77 GB / 0 free]
PV /dev/hdc2 VG Ubuntu lvm2 [28.52 GB / 28.52 GB free]
Total: 3 [59.09 GB] / in use: 3 [59.09 GB] / in no VG: 0 [0 ]

root@borkstation32:/home/ubuntu# lvextend -L+28G /dev/Ubuntu/root
Extending logical volume root to 57.70 GB
Logical volume root successfully resized

lvextend -L+528M /dev/Ubuntu/root
Extending logical volume root to 58.21 GB
Logical volume root successfully resized

e2fsck -f /dev/Ubuntu/root
resize2fs /dev/Ubuntu/root

You can check the new size with mount /dev/Ubuntu/root /mnt and then df
and reboot :)
All was don with an live cd (my root partition is on the lvm so i had to take it offline)