LVM Hands-on Tutorial: Extend Disks, Create LVMs, Snapshots

This tutorial walks through a complete LVM demonstration using a KVM virtual machine. It includes:

• Creating a VM
• Attaching new disks
• Creating Physical Volumes (PVs), Volume Groups (VGs), Logical Volumes (LVs)
• Mounting and resizing
• Creating and restoring LVM snapshots

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First thing first, we will clone any Linux VM. In my case, I am going with Ubuntu 24.04 CLI

Clone the master VM image:

virt-clone --original <source-vm> --name LVM-Tutorial-VM \
  --file <destination-path>/LVM-Tutorial-VM.qcow2

Step 1: Create VM from Master Copy

virsh start LVM-Tutorial-VM

Step 2: Create and Attach First Additional Disk

qemu-img create -f qcow2 -o preallocation=metadata \
  /<path-to-your-disk>/LVM-Tutorial-VM_disk2.qcow2 20G

virsh attach-disk --domain LVM-Tutorial-VM \
  --source /<path-to-your-disk>/LVM-Tutorial-VM_disk2.qcow2 \
  --target vdb --persistent --targetbus virtio

Login into VM:

virsh console LVM-Tutorial-VM

Step 3: Create Physical Volume and Volume Group

sudo pvcreate /dev/vdb
sudo vgcreate vg_data /dev/vdb
sudo vgdisplay vg_data

Step 4: Create Logical Volume and Format

sudo lvcreate -L 10G -n lv_data vg_data
sudo lvdisplay

Create a new ext4 filesystem on the logical volume /dev/vg_data/lv_data.

sudo mkfs.ext4 /dev/vg_data/lv_data

Step 5: Mount and Use the Volume

sudo mkdir /data
sudo mount /dev/vg_data/lv_data /data

Adding the UUID entry to the /etc/fstab file ensures that the logical volume is automatically mounted at boot time. Without this, you'd need to manually mount the volume every time the system restarts.

Using the UUID (instead of device paths like /dev/vg_data/lv_data) is a more reliable and persistent method, as device names can change across reboots or if hardware changes occur. The UUID uniquely identifies the filesystem and helps avoid mount failures due to dynamic device naming.

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Step 6: Add Another Disk and Extend LV

Create and attach a second disk:

qemu-img create -f qcow2 -o preallocation=metadata \
  /mnt/qa220250516104235_prashant_test_July_03/LVM-Tutorial-VM_disk3.qcow2 20G

virsh attach-disk --domain LVM-Tutorial-VM \
  --source /mnt/qa220250516104235_prashant_test_July_03/LVM-Tutorial-VM_disk3.qcow2 \
  --target vdc --persistent --targetbus virtio

Inside VM:

sudo pvcreate /dev/vdc
sudo vgextend vg_data /dev/vdc
sudo lvextend -l +100%FREE /dev/vg_data/lv_data
sudo resize2fs /dev/vg_data/lv_data

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Step 7: Add Third Disk and Reserve for Snapshots

qemu-img create -f qcow2 -o preallocation=metadata \
  /mnt/qa220250516104235_prashant_test_July_03/LVM-Tutorial-VM_disk4.qcow2 30G

virsh attach-disk --domain LVM-Tutorial-VM \
  --source /mnt/qa220250516104235_prashant_test_July_03/LVM-Tutorial-VM_disk4.qcow2 \
  --target vdd --persistent --targetbus virtio

Now I have added another disk size of 30G vdd for showcasing the snapshot feature

Inside VM:

sudo pvcreate /dev/vdd
sudo vgextend vg_data /dev/vdd
sudo lvextend -L +15G /dev/vg_data/lv_data
sudo resize2fs /dev/vg_data/lv_data

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Now create a file in the /data directory

cd /data
touch demo.txt
echo "Initial content" | tee demo.txt

Step 8: LVM Snapshot Demo

Create snapshot:

sudo lvcreate -L 10G -s -n lv_data_snap /dev/vg_data/lv_data

Modify data under /data...

Restore from snapshot:

sudo umount /data
# If busy:
sudo fuser -km /data

sudo lvchange -an /dev/vg_data/lv_data
sudo lvconvert --merge /dev/vg_data/lv_data_snap
sudo lvchange -ay /dev/vg_data/lv_data
sudo mount /dev/vg_data/lv_data /data

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Detach Disk (optional cleanup)

virsh detach-disk --domain LVM-Tutorial-VM --target vdb --persistent
virsh detach-disk --domain LVM-Tutorial-VM --target vdc --persistent
virsh detach-disk --domain LVM-Tutorial-VM --target vdd --persistent

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Conclusion

You successfully:

• Created a VM
• Attached multiple disks
• Configured LVM from scratch
• Extended LVs live
• Demonstrated LVM snapshot and recovery

Authored by Prashant S.B.