📘 LVM (Logical Volume Manager)¶

What is LVM?¶

LVM (Logical Volume Manager) is a storage management system in Linux that adds an abstraction layer between physical storage devices and filesystems.

Its main purpose is to make disk storage:

Flexible
Expandable
Easier to manage

Instead of working directly with fixed disk partitions, LVM allows administrators to work with logical storage units that can be resized and reorganized easily.

Why LVM Is Needed¶

Traditional disk partitioning has limitations:

Partitions have fixed sizes
Expanding storage often requires downtime
Adding new disks is difficult
Disk space cannot be easily shared

LVM overcomes these limitations by separating:

Physical storage from
Logical storage

This separation allows dynamic storage management.

LVM Storage Layers¶

LVM is built using multiple logical layers. Each layer has a specific role.

Physical Disk → Physical Volume → Volume Group → Logical Volume → Filesystem → Mount Point

1. Physical Disk¶

A physical disk is a real storage device such as:

Hard disk
SSD
Virtual disk

It provides raw storage capacity but has no understanding of files or directories.

2. Partition (Optional Layer)¶

A partition is a defined section of a physical disk.

Although LVM can work directly on entire disks, partitions are often used for:

Organization
Compatibility
Disk layout clarity

Partitions act as containers that can later be managed by LVM.

3. Physical Volume (PV)¶

A Physical Volume (PV) is a disk or partition that has been initialized for use by LVM.

When a PV is created:

LVM writes metadata on it
The space is divided into equal-sized blocks called Physical Extents

A PV is the basic building block of LVM.

4. Volume Group (VG)¶

A Volume Group (VG) is a storage pool created by combining one or more Physical Volumes.

Key characteristics:

Aggregates total storage capacity
Can grow by adding more PVs
Acts as a single large storage unit

The VG hides the complexity of multiple disks.

5. Logical Volume (LV)¶

A Logical Volume (LV) is a virtual storage unit created from a Volume Group.

Characteristics:

Acts like a traditional disk partition
Can be resized
Can span multiple physical disks
Used to store filesystems

Logical Volumes are the main objects users interact with in LVM.

6. Filesystem¶

A filesystem defines how data is stored and organized on a Logical Volume.

Responsibilities:

Manages files and directories
Handles permissions and metadata
Controls space allocation

Common filesystems include ext4 and XFS.

7. Mount Point¶

A mount point is a directory in the Linux filesystem hierarchy where a filesystem is attached.

Once mounted:

Data on the Logical Volume becomes accessible
The filesystem integrates into the system’s directory tree

Internal LVM Concepts¶

Extents¶

Physical Extents (PE): Fixed-size blocks on a Physical Volume
Logical Extents (LE): Mapped blocks used by Logical Volumes

LVM maps LEs to PEs dynamically, enabling flexibility and resizing.

Key Advantages of LVM¶

Dynamic resizing of storage
Ability to add disks without downtime
Improved storage utilization
Support for snapshots
Better abstraction of physical hardware

Summary¶

LVM separates physical storage from logical usage
Storage is managed in layers
Logical Volumes provide flexibility over traditional partitions
Filesystems operate on LVM, not directly on disks

Create and Mount an LVM Volume on a New Disk¶

Attach a Virtual Disk to Your Hyper-V VM¶

Shut down the VM.
Open Hyper-V Manager.
Right-click on the VM and select Settings.
Under Hardware, select SCSI Controller (or add one if it's not there already).
Click Add > Hard Drive > New.
Choose VHDX or VHD, set the size for the new virtual disk, and click OK.
Start the VM.

LVM Setup Steps¶

1. Verify the New Disk¶

Check if the new disk is visible to the system:

lsblk
fdisk -l

Example output:

sdb       8:16   0  100G  0 disk

2. Create a New Partition¶

Use fdisk to create a Linux partition on /dev/sdb:

fdisk /dev/sdb

Inside fdisk, perform the following: - Press n → create a new partition - Press p → primary partition - Accept defaults for sector unless specific sector sizes are needed - Define size, e.g.: +95G - Press w → write changes and exit

Verify the new partition:

fdisk -l /dev/sdb

You should now have /dev/sdb1.

3. Create a Physical Volume (PV)¶

pvcreate /dev/sdb1

Confirm:

pvs
pvsdisplay

4. Create a Volume Group (VG)¶

vgcreate earth_volume_group /dev/sdb1

Check VG details:

vgdisplay

5. Create a Logical Volume (LV)¶

Allocate 90 GB for the new logical volume:

lvcreate -L 90G -n my_logical_volume earth_volume_group

List LVs:

lvs

Confirm LV path:

/dev/earth_volume_group/my_logical_volume

6. Create a Filesystem on the LV¶

Format the logical volume with the ext4 filesystem:

mkfs.ext4 /dev/earth_volume_group/my_logical_volume

7. Create a Mount Directory¶

mkdir -p /HOME

8. Mount the New Filesystem¶

mount /dev/earth_volume_group/my_logical_volume /HOME

9. Verify the Mount¶

df -Th

Expected output:

/dev/mapper/earth_volume_group-my_logical_volume  ext4  89G   24K  84G  1% /HOME

10. Make the Mount Persistent¶

Before editing /etc/fstab, always back it up:

cp /etc/fstab /etc/fstab.bak

Get the UUID of the newly formatted LV:

blkid /dev/earth_volume_group/my_logical_volume

Example output:

/dev/earth_volume_group/my_logical_volume: UUID="6a62873b-95f8-4252-b73d-82daa7378b11" TYPE="ext4"

Copy the UUID shown for the device. Edit /etc/fstab:

vi /etc/fstab

Add this line at the end (replace <UUID> with the actual UUID):

UUID=<UUID>  /HOME  ext4  defaults  0  0

11. Test the fstab Entry¶

Unmount and remount to ensure the entry works:

umount /HOME
mount -a
df -Th

You should see /HOME mounted automatically.

LVM Structure Diagram¶

[Physical Disk: /dev/sdb]
          │
          ▼
[Partition: /dev/sdb1] ← we have to create
          │
          ▼
[Physical Volume (PV): /dev/sdb1] ← we have to create
          │
          ▼
[Volume Group (VG): earth_volume_group] ← we have to create
          │
          ▼
[Logical Volume (LV): my_logical_volume] ← we have to create
          │
          ▼
[Filesystem: ext4]
          │
          ▼
[Mount Point: /HOME]

LVM Components Summary¶

Physical Disk: The entire disk device.
Partition: Disk section created with fdisk, e.g., /dev/sdb1.
Physical Volume (PV): LVM-initialized partition, e.g., after pvcreate /dev/sdb1.
Volume Group (VG): Pool of storage created by combining PV(s), e.g., earth_volume_group.
Logical Volume (LV): Virtual disk partition allocated from VG, e.g., my_logical_volume.
Filesystem: Format the LV with a filesystem like ext4.
Mount Point: Directory to access the data, e.g., /HOME. ```