Shrink LVM partition

Since I’m a quiet crazy guy I worked this guide out without a backup of my data.
!!! DONT’T BE SO STUPID LIKE ME !!!
Anyway everything went smooth. But don’t cry if you are trashing all your data!

I have the following disk:

Disk /dev/sda: 100.0 GB, 100030242816 bytes
255 heads, 63 sectors/track, 12161 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1               1          26      204819+  ee  EFI GPT
/dev/sda2              26         662     5111808   af  Unknown
/dev/sda3   *         662         675      102400   83  Linux
/dev/sda4             675       12161    92264204+  8e  Linux LVM

lvm vgchange -a y
e2fsck -f /dev/VolGroup00/LogVol00
resize2fs -f /dev/VolGroup00/LogVol00 10G
e2fsck -f /dev/VolGroup00/LogVol00

Now display the the Logical Volume (it is still 86.00 GB) lets reduce it also to 40G

lvm lvdisplay /dev/VolGroup00/LogVol00
lvm lvreduce -L10G /dev/VolGroup00/LogVol00
lvm lvdisplay /dev/VolGroup00/LogVol00

Now it is 40.00 GB

mount /dev/VolGroup00/LogVol00 /mnt/source
umount /mnt/source

lvm lvdisplay

as you can see we have now two logical volumes (LogVol00 40.00 GB and LogVol01 1.94GB)

lvm vgdisplay

we have free PE 46.03 GB and allocated PE 41.94 GB

First find the LVM-Partition with

fdisk /dev/sda

Note: our partition is sda4

lvm pvresize --setphysicalvolumesize 41.94G /dev/sda4