Linux Logical Volume Manager (LVM) Deep Dive Tutorial

LVM, short for Logical Volume Manager, is awesome – and it doesn’t seem to get the attention it deserves. In this one-shot tutorial, I’ll show you why you should care about LVM, how to get started, some of the commands you can use to manage it, and more. You’ll even learn how to use it to take snapshots of your system!

YouTube player

Commands Used

Resizing a logical volume

First, get a tiny bit of space back for tmp files (this command clears apt caches and etc):

sudo apt clean

Extend the logical volume

lvextend --resizefs -l +100%FREE /dev/mapper/vg_ubuntu-lv_root

Adding a disk to LVM

After adding a physical or virtual disk to the server, run the following commands.

Convert the new disk to an LVM physical volume

Note: Make sure you change “sdb” to the identifier of your drive):

pvcreate /dev/sdb
Add the new physical volume to the volume group
vgextend vg_ubuntu /dev/sdb
Check the status
Extend the physical volume by 10GB (or however many “GB” you want)
lvextend -L +10G /dev/mapper/vg_ubuntu-lv_root
Grow the logical volume with ALL of the available space, without specifying a particular size
lvextend --resizefs -l +100%FREE /dev/mapper/vg_ubuntu-lv_root
Grow the filesystem to match the newly available space
resize2fs /dev/mapper/vg_ubuntu-lv_root
Check current available space
 df -h

Creating a brand-new LVM setup

Add a new virtual or physical disk to the server.

Note: For all of the below commands, change “sdc” to match your disk’s identifier

Convert the new disk to be an LVM physical volume

pvcreate /dev/sdc

Create the volume group

vgcreate vg_extra /dev/sdc

Check the volume group


Create a logical volume (named lv_logs in this example)

lvcreate vg_extra -L 5G -n lv_logs

Format the logical volume

mkfs.ext4 /dev/mapper/vg_extra-lv_logs

Create a directory to mount the new logical volume

mkdir /mnt/extra/logs

Mount the logical volume

mount /dev/mapper/vg_extra-lv_logs /mnt/extra/logs

Find the “block id” of the new logical volume

blkid /dev/mapper/vg_extra-lv_logs

Back up your fstab file to be safe

cp /etc/fstab /etc/fstab.bak

Edit the fstab file

nano /etc/fstab
Add a line to the fstab to mount the volume, similar to this
UUID=<BLOCK ID FOR LOGICAL VOLUME> /mnt/extra/logs ext4 defaults 0 2
Test the new mount, first making sure it’s not mounted
umount /mnt/extra/logs
Then test your fstab file (BEFORE rebooting)
mount -a

If no errors, then you’re all set.


Create a new snapshot

lvcreate /dev/mapper/<SOURCE VOLUMEGROUP NAME> -L 1G -s -n snapshot_name

View used space of snapshots


Mount a snapshot

mount /dev/mapper/vg_extra-web_snapshot_20200421 /mnt/extra/snapshot

Restore a snapshot

Umount the original volume:

umount /path/to/mounted/logical-volume

Restore the snapshot:

lvconvert --merge /dev/mapper/snapshot_name

Deactivate/reactivate to fresh it:

lvchange -an /dev/mapper/vg_extra-lv_web
lvchange -ay /dev/mapper/vg_extra-lv_web

Notable Replies

  1. In this video at around 46:00 it shows that there’s a snapshot logical volume created with 1Gb of space. However, it’s taking the snapshot of another logical volume of 5Gb. In this example there was only one file so I guess this may seem like a silly question… but do LVM snapshots ignore unused/free space in the target logical partition?

  2. LVM snapshots require free space in the Volume Group, not on the Logical Volume. Run vgs and check your vg’s size. It should say that free space is not 0, in order to take snapshots. If you run out of space on the vg, the snapshot becomes useless, because it can’t move the old data to another location. You should keep at least 15% free space in the volume group for lvm snapshots and 10% free to allocate to logical volumes in a pinch if you run production, although you can just add a new disk, or for a VM increase the size of the current disk, create a new partition and expand the logical volume that way.

  3. Thanks, I still haven’t tested this but will it give a try. I was just confused about that difference in size reported.

  4. Volume management is not too hard. The partition is how you partition the disk. Then you create physical volumes on the partitions.

    Then you make the volume groups. To each volume group, you can have as many as you want, you assign an amount of space from the physical volume. But to a logical volume, it is like a virtual partition, you consider the volume group like a custom size storage device, like a custom virtual hdd, and you partition it in smaller chunks for different mounts, called logical volumes.

    Using “virtual hdds” is easier to manage, especially when you want to move things around. It also eliminated some of the old problems with MBR (like limited number of partitions).

  5. The theory seems pretty straight forward, although I’m curious about practical use cases. For example, now that we have modern file systems like btrfs, wouldn’t it be better to use that for snapshots?

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