Mastering LVM on Linux: Step‑by‑Step Guide to Create, Extend, and Snapshot Logical Volumes

What is LVM?

LVM (Logical Volume Manager) is a Linux storage subsystem that aggregates physical disks or partitions into a single storage pool, allowing dynamic resizing of volumes and more efficient use of disk space.

LVM Components

Physical Volume (PV) : a disk or partition that becomes part of the pool.

Volume Group (VG) : a collection of one or more PVs, treated as a single logical disk.

Logical Volume (LV) : a slice of a VG that can be formatted and used for data storage.

Physical Extent (PE) : the smallest allocation unit inside a VG (default 4 MiB, configurable).

Creating and Removing Physical Volumes

Assuming two unused disks /dev/sdb and /dev/sdc: # pvcreate /dev/sdb /dev/sdc To delete a PV later:

# pvremove /dev/sdc

Creating a Volume Group

Combine the two PVs into a VG named my_vg with a 4 MiB PE size: # vgcreate -s 4M my_vg /dev/sdb /dev/sdc Verify with:

# vgs

Extending a Volume Group

Add a new PV /dev/sdd to the existing VG:

# vgextend my_vg /dev/sdd

Removing a Physical Volume from a VG

Detach /dev/sdd from my_vg:

# vgreduce my_vg /dev/sdd

Removing an Entire Volume Group

Delete the VG my_vg completely:

# vgremove my_vg

Removing an Empty VG

If a VG has no allocated LVs, it can be removed automatically:

# vgreduce -a my_vg

Creating a Logical Volume

Create a 10 GiB LV named my_lv inside my_vg: # lvcreate -L 10G -n my_lv my_vg List LVs to confirm:

# lvs

Formatting and Mounting the LV

# mkdir /LVM
# mkfs.ext4 /dev/my_vg/my_lv
# mount /dev/my_vg/my_lv /LVM

Extending an LV

Increase the LV size by 5 GiB, then resize the filesystem:

# lvextend -L +5G /dev/my_vg/my_lv
# resize2fs -f /dev/my_vg/my_lv

Check the new size with df -h.

Reducing an LV

To shrink the LV back to 10 GiB, unmount, check, resize the filesystem, then reduce the LV:

# umount /dev/my_vg/my_lv
# e2fsck -f /dev/my_vg/my_lv
# resize2fs -f /dev/my_vg/my_lv 10G
# lvreduce -L 10G /dev/my_vg/my_lv

Confirm the new size with df -h.

Taking a Snapshot

Create a 200 MiB snapshot of my_lv named mylv_back:

# lvcreate -s -n mylv_back -L 200M /dev/my_vg/my_lv

List snapshots with lvs.

Restoring from a Snapshot

Mount the snapshot and copy its contents back to the original location:

# mkdir /back
# mount /dev/my_vg/mylv_back /back
# cp -a /back/* ./