What is LVM?

LVM is a special tool in Linux that let’s you manage disk storage in much more flexible way than traditional partitions.

Think of it as turning multiple hard drives into a big, flexible stroage pool that you can split, resize, or grow whenever you want, without worrying about the limits of classic disk partitions.

Why Use LVM?

Resize storage easily: You can expand or shrink volumes without reformatting or losing data.
Combine multiple disks: Make many drives look like one big storage area.
Add more space anytime: Plug in new hard drive and add its space instantly.
Move or migrate data: Shift storage between drives with little downtime.
Take snapshots: Save the exact state of you data at a moment in time, which helps with backups.

Practical Example

Classic Partitioning (without LVM)

You have 100GB disk with /home and /var partitions.
/home fills up, while /var has lots of free space.
Problem: You can’t take space from /var and give it to /home without migrating, deleting, repartitioning or copying data aroud. Which is possible but risky and time-consuming.

With LVM

Let’s say you have two physical disks:

Disk 1: 100GB
Disk 2: 200GB

You do the following:

Initialize the disks as LVM Physical Volume (PV).
Combine them into a Volume Group (Vg); Eg: testvg, making it a single 300GB storage pool.
Create Logical Volume inside that pool, for example:

lv_home for your /home directory: 150GB.
lv_var for your /var directory: 50GB.

If /home is getting full, you can:

Shrink lv_var to 25GB (only if it has enough space).
Grow lv_home to 175GB.

To add more space in the future:

Plug in a new disk.
Add it to the volume group, after making a physical volume out of it.
Instant make the space available to any logical volume you choose.

Basic Usage

Physical Volume (PV) : Disk/Partition initialized for LVM
Volume Group (VG) : Pool for combining several Physical Volumes (PVs).
Logical Volume (LV): Carved-out “Virtual Partition” for filesystems.

List Information

Physical Volume (PV):

sudo pvs

Volume Group (VG):

sudo vgs

Logical Volume (LV):

sudo lvs

Create PV, VG & LV

Physical Volume (PV):

sudo pvcreate /dev/sda #if only one disk
sudo pvcreate /dev/sda /dev/sdb #if more than one disk

Volume Group (VG):

sudo vgcreate <VG_NAME> /dev/sda #if only one physical volume to add

Logical Volume (LV):

sudo lvcreate -n <LV_NAME> -L 8G <VG_NAME>

Remove PV, VG & LV

Physical Volume (PV):

sudo pvremove /dev/sda #if only one disk
sudo pvremove /dev/sda /dev/sdb #if more than one disk

Volume Group (VG):

sudo vgremove <VG_NAME>

Logical Volume (LV):

sudo lvremove /dev/<VG_NAME>/<LV_NAME>
#example
sudo lvremove /dev/allvg/lv_home

Modifying Storage Size

Extending an LVM Logical Volume (No Downtime, Safe)

Check available space in the volume group and decide the amount to extend the size.

sudo vgs
sudo vgdisplay # for more detail

Extend the logical volume (lv_home)

Add 2GB

sudo lvextent -L +2G /dev/allvg/lv_home

Modern LVM also supports percentage

sudo lvextend -l +100%FREE /dev/allvg/lv_home

Resize the filesystem after the extending the volume group

sudo resize2fs /dev/allvg/lv_home
# do this while it's mounted

Note:resize2fs simply updates the metadata and structure to reflect the bigger Logical Volume after a resize.

Note: Filesystem can be grown while mounted for ext4/xfs

Basically, the space is coming from the volume group (allvg), so I’m using vgdisplay to check the available Free PE/Size.
Then, we can use lvextend -L +2G ... to extend the space based on the Free PE/Size you have.
Lastly, use resize2fs to update the partition table.

Output of vgdisplay:

iamyaash@pi5:~ $ sudo vgdisplay 
  --- Volume group ---
  VG Name               allvg
  System ID             
  Format                lvm2
  Metadata Areas        1
  Metadata Sequence No  2
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                1
  Open LV               1
  Max PV                0
  Cur PV                1
  Act PV                1
  VG Size               <8.00 GiB
  PE Size               4.00 MiB
  Total PE       r       2047
  Alloc PE / Size       1024 / 4.00 GiB
  Free  PE / Size       1023 / <4.00 GiB
  VG UUID               4KP5xQ-icGT-1G0L-hr8S-2oMc-1cuQ-y71xAz

Shrinking an LVM Logical Volume (Caution!)

Reducing a volume is riskier, always backup before you do anything!

Unmount the filesystem, because it’s not possible to shrink while it’s mounted:

sudo umount /mnt/lv_home

Perform a forced filesystem check (mandatory):

sudo e2fsck -f /dev/allvg/lv_home

Shrink the filesystem

Reduce to 4GB Total Size

sudo resize2fs /dev/allvg/home 4G

Reduce the Logical Volume:

sudo lvreduce -L 4G /dev/allvg/lv_home

Note: Never reduce the LV before shrinking the filesystem.

Remount and verify:

sudo mount /dev/allvg/lv_home
df -h /mnt/lv_home

How to Initialize a Disk with LVM

Ensure you format the disk, and prepare it for partitioning:

lsblk #list the block of partitions
sudo mkfs.ext4 /dev/sda #ext4 format

Create Partition Using parted:

sudo parted /dev/sda

mklabel gpt #set partition table to GPT
mkpart primary ext4 1MiB 80GiB #create 8GB partition
name 1 gpt_home #set partition label
quit # save/write the chages for partitions

Note: Make sure to use ext4, as it is most recommended format.

# list the available partitions
lsblk

To Remove the Partition:

sudo parted /dev/sda
rm 1 #to remove the partition number 1 (i.e: sda1)

Create Physical Volume

sudo pvs # list any avail PVs
sudo pvdisplay # more details

sudo pvcreate /dev/sda1 # select the sda1 which is the 80GB partition

Create Volume Group

sudo vgs
sudo vgdisplay

sudo vgcreate allvg /dev/sda1 # create a new VG name and select the partition as well

Create Logical Volume

sudo lvs # list the available LVs
sudo lvdisplay

sudo lvcreate -n lv_home -L 44G allvg # create 44GB LV with LV name as lv_home

Scan the disk for LVM usage:

sudo lvmdiskscan

Format the LV (Virtual Partition) as ext4:

sudo mkfs.ext4 /dev/allvg/lv_home

Mount Logical Volume

sudo mkdir /mnt/lv_home
sudo mount /dev/allvg/lv_home /mnt/lv-home

Mount Automatically At Boot

lsblk -f # list partition blocks along with other information such as UUID
# or
blkid | grep dev/sda # to see all UUIDs

Locate the UUID of you logical volume, especially note the ext4 format UUID not the LVM_Member.

sudo nano /etc/fstab

Add this line into /etc/fstab:

UUID=44bbb6b2-803e-4009-b8f5-e4fbcd743aff /mnt/lv_home ext4 defaults 0 2

How to Fully Reinitialize a Disk (In case you messed up)

Ensure your disk is not mounted or used by your operating system, because these steps destroy all data on the disk(s) involved.

Unmount Logical Volumes, if mounted:

sudo umount /mount/point

Remove Logical Volume (LV)

# list the available LVs
sudo lvs
# remove the selected LV
sudo lvremove /dev/<VG_NAME>/<LV_NAME>

Remove the Volume Group (VG)

# list the available VGs
sudo vgs
# remove the selected VG
sudo vgremove <VG_NAME>

Remove the Physical Volume (PV)

# list the available PVs
sudo pvs
# remove the PV
sudo pvremove /dev/sdX

Substitute /dev/sdX with your partition name where the PV is created.

Remove Partitions To Start Fresh

Use tools like mkfs to format and fdisk or parted to create partitions.

What is LVM?#

Why Use LVM?#

Practical Example#

Classic Partitioning (without LVM)#

With LVM#

Basic Usage#

List Information#

Create PV, VG & LV#

Remove PV, VG & LV#

Modifying Storage Size#

Extending an LVM Logical Volume (No Downtime, Safe)#

Shrinking an LVM Logical Volume (Caution!)#

How to Initialize a Disk with LVM#

How to Fully Reinitialize a Disk (In case you messed up)#

What is LVM?

Why Use LVM?

Practical Example

Classic Partitioning (without LVM)

With LVM

Basic Usage

List Information

Create PV, VG & LV

Remove PV, VG & LV

Modifying Storage Size

Extending an LVM Logical Volume (No Downtime, Safe)

Shrinking an LVM Logical Volume (Caution!)

How to Initialize a Disk with LVM

How to Fully Reinitialize a Disk (In case you messed up)