How to reduce Volume Group size in LVM?

These are the steps required to resize an LVM or LVM2 partition:

sudo lvresize --verbose --resizefs -L -150G /dev/ubuntu/root

sudo pvresize --setphysicalvolumesize {any size here} /dev/sda5

The last command, pvresize, may yield the error

/dev/sda5: cannot resize to xxxxx extents as later ones are allocated.

You have to rearrange the unallocated space at the end of the LVM. That means after root and swap_1 partition. You can see the current arrangement of space with this command

pvs -v --segments /dev/sda5

pvs will show output like this

/dev/sda5 ubuntu lvm2 a-- 698.04g 150g 0 xxx+1 root 0 linear /dev/sda:0-xxx
/dev/sda5 ubuntu lvm2 a-- 698.04g 150g xxx+1 iii 0 free
/dev/sda5 ubuntu lvm2 a-- 698.04g 150g yyyy jjj swap 0 linear /dev/sda5:yyyy-end

Now use pvmove to remove external fragmentation:

sudo pvmove --alloc anywhere /dev/sda5:yyyy-end

Now let's see if moving the swap volume succeeded.

pvs -v --segments /dev/sda5

should show the new order of volumes:

/dev/sda5 ubuntu lvm2 a-- 698.04g 150g 0 xxx+1 root 0 linear /dev/sda:0-xxx
/dev/sda5 ubuntu lvm2 a-- 698.04g 150g xxx+1 iii swap 0 linear /dev/sda5:xxx+1-yyyy
/dev/sda5 ubuntu lvm2 a-- 698.04g 150g yyyy+1 end 0 free

After that, use GParted and resize the LVM to the maximum used area. The rest will be in unallocated space.

You can use pvmove to move those extents to the beginning of the device or another device:

sudo pvmove --alloc anywhere /dev/device:60000-76182

Then pvmove chooses where to move the extents to, or you can specify where to move them.

See pvs -v --segments /dev/device to see what extents are currently allocated.