lvm.txt

#To see partitions
sudo fdisk -l (cat /proc/partitions) (lsblk)
(Let's say you see three devices)
/dev/xvdf, /dev/xvdj, /dev/xvdg
# To reread partitions
partprobe /dev/sdX (or just partprobe)

#If not already installed
sudo apt-get install lvm2

# Create an lvm partition. 
gdisk -l /dev/loop0
n
(select size)
L (to lookup the codes)
8e00	(lvm type)
w

#sync
partprobe /dev/xxxx


#Create lvm
pvcreate /dev/xvdf /dev/xvdj /dev/xvdg (physical volume created)
vgcreate ghumVol /dev/xvdf /dev/xvdj /dev/xvdg (volume group created)
lvcreate -l 100%FREE -n devdisks ghumVol (logical volume created)

#Display logical volume
lvdisplay
(or) lvs

#Put filesystem
(Install ext4 if shrinking and growing is needed at a later stage)
(xfs doesn't allow shrinking of filesystem, it can only grow)
mkfs.ext4 /dev/ghumVol/devdisks

#Mount
mkidr /mnt/newvol
sudo mount /dev/ghumVol/devdisks /mnt/newvol

#Note
Just like encrypting partitions create /dev/mappers/xxxx, lvm also creates devices with symlink inside /dev/mappers and also /dev/vgdata/lvdata.

# change properties of filesystems which are already created use tune2fs
tune2fs  -L lvdata /dev/vgdata/lvdata

#mounting using Labels in /etc/fstab
LABEL=lvdata	/lvmount/point	ext4	defaults	0 0

#mounting using UUID in /etc/fstab
#to find out uuid of filesystem, use "blkid" (can use with double quotes or without it)
UUID="xxxxxxxxxxxxxx"	/lvmount/point	ext4	defaults	0 0

# Resize LVM
pvs, vgs, lvs  show size and free space
i) create new partition using gdisk/pdisk (using LVM partition)
ii) vgextend vgdata /dev/newlycreated
(above command detects that newly created partition is not physical volume so it converts it to physical volume and then adds it to vgdata volume group)
iii) lvextend -l +100%FREE -r /dev/vgdata/lvdata (r for resize)

# Shrink
lvreduce -L 800M -r /dev/vgnew/lvnew
(it will ask permission to unmount, then will resize and will mount it again)