Lab: LVM, fstab and online extension

What you will learn in this TP

• Create PVs, VGs and LVs
• Mount by UUID in fstab
• Extend online and take a snapshot

Introduction #

What you will learn in this section

• Create PVs, VGs and LVs
• Mount by UUID in fstab
• Extend online and take a snapshot

Context. An application's data volume is filling up. You set up LVM storage that can grow without downtime. Disks are simulated with files (loop devices): nothing touches the real disks.

Prerequisites: a disposable Ubuntu 24.04 virtual machine (Multipass, Vagrant or cloud) with a sudo account  ·  Estimated time: 50 min

A /data volume grown from 600 MB to 1.4 GB without unmounting.

Hands-on #

Guided steps, with their solution.

1. 1. Create two virtual disks

   Why? Loop devices let you practise without risk to the system disk.

   Create two 1 GB files and attach them as loop devices. Keep their names in variables D1 and D2.

2. 2. Create the logical volume

   Why? The VG is a pool; allocate only what the LV needs to keep headroom.

   Initialise $D1 as a PV, create VG vg_tp and a 600 MB LV lv_data formatted as ext4, mounted on /data.

3. 3. Make the mount persistent

   Why? An fstab mistake can block boot: always check with findmnt and mount -a.

   Add /data to /etc/fstab with its UUID and the nofail option, check the file, unmount and remount with mount -a.

4. 4. Fill the volume

   Why? Simulate data growth to see the need for extension.

   Write a 450 MB file to /data and check usage. Leave an application writing to the volume.

5. 5. Extend online

   Why? With LVM, you add space without unmounting or stopping the application.

   Add $D2 to the VG, extend lv_data by 800 MB growing the file system in the same command, and check writing continues.

6. 6. Take a snapshot

   Why? A snapshot freezes the volume for a consistent backup or a rollback.

   Create a 200 MB snapshot, mount it read-only, compare app.log with the original, then delete the snapshot.

7. 7. Clean up

   Why? Undo cleanly in reverse order: mount, LV, VG, PV, loop.

   Stop the writer, unmount, remove the fstab line and delete LVM and the loop devices.

Difficulty level : ●●●○○ (3/5)