* DISCLAIMER: this is my personal note. use at your own risk.

* My home machine is running Devuan
- note: mount | grep -v -E "/sys|tmpfs|proc|devpts|gvfs"
- current disk layout on /dev/sda (GPT):
  = p1: UEFI partition (fat32) 127M (1M offset)
  = p2: Root partition (ext4) 30G
  = p3: Home partition (ext4) ~898G
  = p4: Swap partition (swap) 4G

@ TASK: Create a new lv from slice of p3
- make sure basic lvm terms/concepts are covered
  = volume group (vg)
  = physical volume (pv) [aix:pv MUST BE a disk]
  = physical element/extent (pe) [aix:pp=physical partition]
  = logical volume (lv)
  = logical element/extent (le) [aix:lp=logical partition]
- need to unmount /home
  = login as root and make sure no user logged in
- target disk layout:
  = p1: UEFI partition (fat32) 127M (1M offset)
  = p2: Root partition (ext4) 30G
  = p3: Home partition (ext4) 600G
  = p4: Xtra partition (lvm) ~298G
  = p5: Swap partition (swap) 4G
- current p3 content is <500G

* repartition disk to create space for new lv
# umount /home
# e2fsck -f /dev/sda3
# resize2fs -p /dev/sda3 500G
# swapoff /dev/sda4
# gdisk /dev/sda
> delete /dev/sda4
> note /dev/sda3 starting sector
> delete /dev/sda3
> create new /dev/sda3 (linux:8300)
  = make sure use same starting sector
  = specify size +600G
> create new /dev/sda4 (linux lvm:8e00)
  = default starting sector
  = specify -4G to leave space for swap
> create new /dev/sda5 (swap:8200)
  = should have 4G remaining
> exit
* reclaim /dev/sda3 space (600G)
# resize2fs -p /dev/sda3
* edit /etc/fstab accordingly
  - e.g. specify new uuid for swap & /dev/sda3
* restore swap
# swapon -a
- OR, 'swapon /dev/sda5'

* install lvm
- using lvm2 implementation (uses device mapper)
# apt install lvm2

* create pv
# pvcreate /dev/sda4
* create volume group vg
# vgcreate xtravg /dev/sda4
* playing around (create/remove lv)
# lvcreate -L 100G -n store xtravg
# lvcreate -l +100%FREE -n movie xtravg
# lvremove movie
# lvremove store

* create single lv on vg
# lvcreate -l +100%FREE -n share xtravg
# vgdisplay xtravg
* create ext4 fs on lv
# mkfs.ext4 -L LVMSHARE /dev/xtravg/share
* create a mountpoint for the new lv
# mkdir /ext
* check entry in /dev/mapper/
  = should have xtravg-share
* add entry in fstab
  = e.g. /dev/mapper/xtravg-share /ext ext4 defaults 0 2
* manually mount
# mount /ext

@ TASK: Add new disk to existing lv
- got a new disk, using whole disk (1TB)
- extend existing lv

# pvcreate /dev/sdb
# vgdisplay xtravg
# vgextend xtravg /dev/sdb
# vgdisplay xtravg
* use all newly available space
# lvextend -l +100%FREE /dev/xtravg/share

@ TASK: Remove PV from VG
- need to use original /dev/sda4 for something else
- note: pvs -o+pv_used
- PV is in use, so need to free up

# umount /ext
# e2fsck -f /dev/xtravg/share
# resize2fs -p /dev/xtravg/share 800G
# lvreduce -L 850G /dev/xtravg/share
* reclaim space
# resize2fs -p /dev/xtravg/share
* check usage
# pvs -o+pv_used
- OR, pvdisplay
* IF any PEs still in use
# pvmove /dev/sda4
* remove pv from vg
# vgreduce xtravg /dev/sda4
* remove pv from system (no longer id as pv)
# pvremove /dev/sda4
* reclaim all lv space
# lvextend -l +100%FREE /dev/xtravg/share
# resize2fs -p /dev/xtravg/share