1. delete partition table

fdisk /dev/sdb
d
w

2. recreate partition table

fdisk /dev/sdb
n
1
enter
p
enter
t
8e       (for LVM)
w

3. rescan

rescan-scsi-bus.sh

4.

kpartx -av /dev/mapper/sdb1

5. resize PV

resizepv /dev/sdb1

You must resize the LVM physical volume after you have reduced the partition on the filesystem with fdisk.

I have not the possibility to confirm the exact steps right now, so you should get someone to review the steps before you perform them.

In case something goes wrong, make sure you have your data backed up.

2. Resize the filesystem

resize2fs -p /dev/VolGroup00/LogVol00 50GB

3. Resize the logical volume

lvresize -L50G /dev/VolGroup/LogVol00

4. Backup partition table

sfdisk -d /dev/sda > /var/tmp/partition-table.txt

5. Delete /dev/sda2 partition

Use fdisk to delete the partition /dev/sda2

6. Create a new /dev/sda2 partition

Create a new partion with the exact same starting offset as your former partition (this should be default) and make it only 50G

7. Resize the LVM Physical Volume

pvresize /dev/sda2