Shrink LVM without data loss

assume we have 3 logical volume: lv1 40GB, lv2 8GB, lv3 200GB in volume group called data. we want to resize lv3 become 180GB. here is the steps:

• booting to single mode
• enter init 1 (type: init 1)
• umount logical volume that you want to resize, e.g. umount /dev/data/lv3
• check the filesystem: e2fsck -f /dev/data/lv3
• resize the filesystem: resize2fs -p /dev/data/lv3 180G
• lvreduce -L -20G /dev/data/lv3

Ref: askubuntu.com