lvm cheatsheet

16 Mar 2019

There are certain commands I keep forgetting no matter how many times I try them, ln, git and the reason for this post, LVM. So, here goes a quick how-to for my future me.

Basics

In order to understand LVM it’s required to have a clear picture of its components.

Physical Volume (PV)

A PV is any block device that can be used as storage, eg: /dev/sda

Volume Group (VG)

A VG is a group of at least one PV, it usually contains several, thought.

Logical Volume (LV)

A LV is a portion (partition) of a VG.

How to set up multiple hard drives as one volume?

Define /dev/sda, /dev/sdb2 and /dev/sdc3 as PVs

$ sudo pvcreate /dev/sda /dev/sdb2 /dev/sdc3

Create a Volume Group (VG) out of three just defined PVs

$ sudo vgcreate vg_name /dev/sda /dev/sdb2 /dev/sdc3

Create a Logical Volume (LV) out of the just defined VG

$ sudo lvcreate -l 100%FREE -n lv_name vg_name

Done!, now it can be formated and mounted as a normal HD, eg:

$ sudo mkfs.ext4 /dev/vg_name/lv_name
$ echo '/dev/vg_name/lv_name /mount_point ext4 defaults 0 0' | sudo tee -a /etc/fstab
$ sudo mount -a

How to mount a previously defined LVM volume

Recreate /dev/ LVM partitions

$ sudo vgchange -ay

Done!, now it can be formated and mounted as a normal HD, eg:

$ sudo mkfs.ext4 /dev/vg_name/lv_name
$ echo '/dev/vg_name/lv_name /mount_point ext4 defaults 0 0' | sudo tee -a /etc/fstab
$ sudo mount -a

How to extend a full LVM volume

First, you need to extend the volume or block in the underlaying VM/Hardware, once done:

$ sudo pvresize /dev/sda #or any other modified device
$ sudo lvextend -l +100%FREE /dev/vg_name/lv_name 
$ sudo resize2fs /dev/vg_name/lv_name  #for ext3/4
$ sudo xfs_growfs -d /dev/vg_name/lv_name #for xfs

That’s it!, I’ll keep adding LVM recipes as I find them, happy storing, 😊

Javier López