LVM backup and restore snapshot in Linux

Logical Volume Manager (LVM) is used on Linux to manage hard drives and other storage devices. As the name implies, it can sort raw storage into logical volumes, making it easy to configure and use.

In this tutorial, you will learn how to create LVM backup and restore in Linux system. LVM works the same on any Linux distribution, so you can use any of the commands below on your own system.

Follow along with us as we use LVM to create partitions, physical volumes, a volume group, logical volumes, and filesystems on a hard disk. We’ll also show how to mount, extend, and remove our newly created logical volumes. At the end of this tutorial, we will take a snapshot of the volume, and then show how to restore the backup.

In this tutorial you will learn:

How to create a logical volume in LVM
How to create a snapshot of a logical volume
How logical volume snapshots work
How to restore a backup of a logical volume

LVM backup and restore snapshot in Linux

Software Requirements and Linux Command Line Conventions
Category	Requirements, Conventions or Software Version Used
System	Any Linux distro
Software	Logical Volume Manager (LVM)
Other	Privileged access to your Linux system as root or via the `sudo` command.
Conventions	# – requires given linux commands to be executed with root privileges either directly as a root user or by use of `sudo` command $ – requires given linux commands to be executed as a regular non-privileged user

LVM backup and restore in Linux step by step

Install LVM on major Linux distros

Your Linux system may already have LVM installed, but it doesn’t come installed by default on every distro. Use the appropriate command below to install LVM with your system’s package manager.

To install LVM on Ubuntu, Debian, and Linux Mint:

$ sudo apt install lvm2

To install LVM on CentOS, Fedora, AlmaLinux, and Red Hat:

$ sudo dnf install lvm2

To install LVM on Arch Linux and Manjaro:

$ sudo pacman -S lvm2

Create partitions

The first thing we will do is create partitions on our disk. This is to facilitate the creation of physical volumes in the next section, which can either be created on raw, unpartitioned block devices or single partitions. For the sake of this tutorial, we will work on the latter.

For this example, the disk we’ll be working with is /dev/sdb, which is a 5GB (and currently unpartitioned) hard disk.

We can see our /dev/sdb disk and its pertinent details with the following command.

# fdisk -l

Use the fdisk command to see the hard disk we will be working with

Next, let’s partition the disk with cfdisk.

# cfdisk /dev/sdb

An interface will open in your console, which is quite intuitive to use. We’ve created the following two partitions as an example.

Write your changes to the disk to finalize the partition table

Finalize your changes by choosing “write,” then exit the utility when done. We can now see our partition listed when we execute fdisk -l again.

Use the fdisk command to see the two partitions we have created

Create physical volumes

We can now create physical volumes on our new partitions by using the pvcreate command.

# pvcreate /dev/sdb1
  Physical volume "/dev/sdb1" successfully created.
# pvcreate /dev/sdb2
  Physical volume "/dev/sdb2" successfully created.

Use the pvdisplay command to see information about all the physical volumes on your system, or specify a particular volume you wish to view details about.

# pvdisplay
OR
# pvdisplay /dev/sdb1

Use pvdisplay command to see a list of physical volumes

Create a volume group

At this stage we need to create a volume group which will serve as a container for our physical volumes. In this example, we’ll call our volume group “mynew_vg” which will include the /dev/sdb1 partition, with the following Linux command:

# vgcreate mynew_vg /dev/sdb1

Or, to include both partitions at once:

# vgcreate mynew_vg /dev/sdb1 /dev/sdb2

Use the following command to display information about the volume group(s).

# vgdisplay

Creating a volume group and then viewing its details

We can add more physical volumes to the group by using the vgextend command.

# vgextend mynew_vg /dev/sdb2
  Volume group "mynew_vg" successfully extended

Create logical volumes

Now we can move on to creating logical volumes. It may help to think of our volume group as a “big cake,” from which we can cut “pieces” (logical volumes) that will get treated as partitions on our Linux system.

The following command will create a logical volume named vol01 with a size of 400MB.

# lvcreate -L 400 -n vol01 mynew_vg

Then, we’ll create another volume named vol02 with a size of 1GB.

# lvcreate -L 1000 -n vol02 mynew_vg

Finally, we can use the lvdisplay command to see the logical volumes we’ve just created.

Using lvdisplay to view information for the two new logical volumes

Create a filesystem on logical volumes

The logical volume is almost ready to use. All we need to do is to create a filesystem on it with the mkfs command.

# mkfs.ext4 -m 0 /dev/mynew_vg/vol01

The -m option specifies the percentage reserved for the super-user, we can set this to 0 to use all the available space (the default is 5%).

Making an ext4 filesystem on the logical volume

Logical Volume Snapshot

Finally, we have come to the point where we can take a snapshot of our logical volume created in the previous sections. For this we will also need some sample data on our Logical Volume “volume1” so once we revert from the snapshot we can confirm the entire process by comparing original data with data recovered from the snapshot.

Understanding Snaphosts

In order to understand how snapshots work, we first need to understand what logical volume consists of and how data is stored. This concept is similar to well known symbolic links. When you create a symbolic link to a file, you are not creating a copy of the actual file but instead you simply create only a reference to it. Logical volume stores data in a similar fashion and it consists of two essential parts:

metadata pointers
data block

When a snapshot is created, Logical Volume Manager simply creates a copy of all Metadata pointers to a separate logical volume. Metadata does not consume much space and therefore you are able to create a snapshot of, let’s say 2GB logical volume to 5MB snapshot volume.

The snapshot volume only starts to grow once you start altering data of the original logical volume. Which means, that every time you remove or edit a file on the original logical volume, a copy of that file (data) is created on the snapshot volume. For a simple change, you may need to create a snapshot volume of around 5-10% of the logical volume original size. If you are prepared to make many changes on your original logical volume then you will need a lot more than 10%.

LVM backup and restore in Linux from Logical Volume Snapshot

Now we are ready to get started. Follow the step by step instructions below to create LVM backup and restore in Linux from the logical volume snapshot.

First, we will create a new mount point for our logical volume, and then mount the volume.
```
$ sudo mkdir -p /mnt/volume1
$ sudo mount /dev/mynew_vg/vol01 /mnt/volume1
```
As mentioned previously, we will need to put some sample data on our logical volume. That way, we can verify that a backup and restore was successful later on. In this step we will simply copy the /usr/bin directory to the volume.
```
$ sudo cp -av /usr/bin/* /mnt/volume1
$ du -s /usr/bin
162528
```
As seen in the output of the du command above, the size of your /usr/bin directory is 162528 bytes in total size. We will use this information for verification that our backup and restore was successfull later.
Now we are going to create a snapshot of logical volume “volume1”. In the process, Logical Volume Manager will create a new separate logical volume. This new logical volume will have size of 20MB and will be called “volume1_snapshot”:
```
$ sudo lvcreate -s -L 20M -n volume1_snapshot /dev/mynew_vg/vol01
  Logical volume "volume1_snapshot" created
```
Now that the snapshot has been created, we can start altering data on “volume1” for example by removing the entire content we copied earlier:
```
$ sudo rm -rf /mnt/volume1/*
```
Next, we use the following lvconvert command to recover our snapshot.

$ sudo lvconvert --merge /dev/mynew_vg/vol01/volume1_snapshot
  Can't merge over open origin volume
  Merging of snapshot volume1_snapshot will start next activation.

After execution of the above command, the logical volume “volume1” will rollback once it is activated. Therefore, what needs to be done next is to re-activate “volume1”. First, make sure that you unmount your the volume we are trying to recover.
```
$ sudo umount /mnt/volume1
```

Now we can deactivate and activate the volume:

$ sudo lvchange -a n /dev/mynew_vg/vol01
$ sudo lvchange -a y /dev/mynew_vg/vol01

For the last step, mount again your logical volume “volume1” and confirm that all of the deleted data has been recovered.
```
$ sudo mount /dev/mynew_vg/vol01 /mnt/volume1
$ du -s /mnt/volume1
162528
```
As evidenced in this output, our logical volume was completely restored to its state at the time of the snapshot.

Closing Thoughts

The above was a basic example of snapshot manipulation using Logical Volume Manager and how to perform LVM backup and restore in Linux. The usefulness of logical volume snapshots is enormous and it will sure help you with your tasks whether you are system administrator or a developer. Although you can use the setup above to create multiple snapshots for a backup recovery, you also need to know that your backup will find its limits within your Logical Volume Group. Therefore, any low level physical volume problems may render your snapshot useless.