Mastering Linux Volume Management (LVM)

Why LVM Matters: Breaking Free from Storage Limitations

Imagine you're building a house with fixed-size rooms. Once constructed, you can't easily expand the kitchen or merge bedrooms. Traditional disk partitioning works similarly—fixed partitions that are hard to modify. Linux Volume Management (LVM) revolutionizes this by letting you create flexible "rooms" (logical volumes) that you can resize, move, or even snapshot while the house is still occupied!

In this comprehensive guide, we'll explore how LVM empowers you to:

• Create storage pools from multiple disks

• Resize filesystems on-the-fly

• Migrate data between physical drives

• Handle cloud storage like a pro

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LVM Core Concepts

1. The Building Blocks: PV, VG, and LV

2. Device Naming in Modern Systems

Linux uses different naming conventions based on storage types:

• /dev/sdX: Classic SATA/SAS drives (sda, sdb...)

• /dev/nvmeXnY: NVMe SSDs (nvme0n1, nvme1n1p2...)

• /dev/xvdX: Common in cloud VMs (xvda, xvdf...)

Pro Tip: Always verify with lsblk before working with disks!

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Real-life Scenario: Expanding Cloud Storage on AWS EC2

Situation

Your web server is running out of space. You need to:

1. Add a new 20GB EBS volume

2. Expand existing storage without downtime

Step-by-step Guide

1. Open your AWS EC2 Dashboard.

2. Go to the Elastic Block Store (EBS) section and create a new volume.

   • Set the Size (GiB) to 20, and Volume Type gp3

   • And MUST specify correct Availability Zone

3. Attach the volume to your EC2 instance as /dev/sdf

NOTE: The region and availability zone must be same for the newly created Volume and EC2 instance (to which you want to Attach the volume).

4. SSH into your instance and verify the new volume:

lsblk

This will list all storage devices. You should see the new volume as /dev/xvdf (or similar).

NOTE: You can follow the below commands as given, but you can also utilize lvm command by first logging in as root, sudo su. After that you can just use those commands without using sudo at prefix.

You can simply write exit to get out of LVM command-line input.

5. Create Physical Volume

sudo pvcreate /dev/xvdf  # Initialize the volume as a Physical Volume
sudo pvs  # Verify

6. Create a Volume Group

sudo vgcreate vg_data /dev/xvdf  # Create Volume Group named vg_data
sudo vgs  # Verify

OR, Extend Volume Group (ONLY IF already exist one and you need to extend specifically that one)

sudo vgextend vg_data /dev/xvdf    # Add to existing VG
sudo vgs  # Check free space (VFree) of the Volume Group

7. Create a Logical Volume

sudo lvcreate -L 20G -n lv_data vg_data   # Create a 20GB LV named lv_data 
sudo lvs  # Verify

OR, Expand Logical Volume (ONLY IF you need to extend an existing Logical Volume)

sudo lvextend -L +20G /dev/vg_data/lv_data

8. Format Logical Volume: Format it to the ext4 filesystem

sudo mkfs.ext4 /dev/vg_data/lv_data

9. Mount the Logical Volume: Create a directory and mount the volume

sudo mkdir /mnt/lv_mount_data
sudo mount /dev/vg_data/lv_data /mnt/lv_mount_data

OR, Resize Filesystem Live (ONLY IF required)

sudo resize2fs /dev/vg_data/lv_data  # For ext4
# For xfs: sudo xfs_growfs /data

Result: Your /data mountpoint now has 20GB more space—no downtime required!

Verify the mount:

df -h

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The Art of Safe Resizing: Let’s Break Down All Possibilities

When Do You Need Formatting?

Formatting prepares a storage device with a filesystem so it can store files. You need to format:

• New physical disks/partitions: Before first use

• Logical Volumes (LVs): After creating an LV

• Changing filesystems: If switching from ext4 to XFS

• Corrupted filesystems: To wipe and start fresh

Example:

# Format /dev/sdb (non-LVM disk) to ext4
sudo mkfs.ext4 /dev/sdb

# Format an LV to XFS
sudo mkfs.xfs /dev/vg_data/lv_data

When Do You Need Mounting?

Mounting makes a filesystem accessible (or usable) to the OS. You need to mount:

• After formatting: To use the storage

• On system reboot: Unless added to /etc/fstab

• Temporary access: e.g., USB drives

Example:

# Mount a formatted disk to /mnt/data
sudo mount /dev/sdb /mnt/disk_mount_data

# Mount an LV
sudo mount /dev/vg_data/lv_data /mnt/lv_mount_data

When Do You Need Resizing?

Resizing adjusts storage capacity dynamically. You need to resize:

• Growing logical volumes: When more space is needed

• Shrinking volumes: Rare, but possible (risky!)

• Cloud storage expansion: After expanding an EBS/GCP disk

• Pooling new disks: Adding PVs to a VG

Example:

# Extend an LV and resize filesystem
sudo lvextend -L +10G /dev/vg_data/lv_data
sudo resize2fs /dev/vg_data/lv_data  # For ext4

Steps To Extend a Logical Volume

1. Check VG free space:

    sudo vgdisplay vg_data | grep "Free PE"
   

2. Extend LV (20GB or 100% free space):

    sudo lvextend -L +20G /dev/vg_data/lv_data  # Specific size
    # OR
    sudo lvextend -l +100%FREE /dev/vg_data/lv_data  # All free space
   

3. Resize filesystem:

    resize2fs /dev/vg_data/lv_data  # ext2/3/4
    xfs_growfs /mountpoint          # XFS
   

To make the mount persistent across reboots, add it to /etc/fstab:

/dev/vg_data/lv_data  /mnt/lv_mount_data  ext4  defaults  0  0

Critical Note: Always resize the filesystem after extending the LV!

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Add Volume Without LVM (Direct Mounting)

Sometimes you don’t need LVM’s flexibility. For example:

• Single-purpose disks (backup drives)

• Temporary storage

• Boot partitions

Step-by-Step Workflow:

1. Identify the disk:

    sudo lsblk
    # Let’s assume the new disk is /dev/sdb
   

2. Format directly (no LVM):

    sudo mkfs.ext4 /dev/sdb
   

3. Create mount point:

    sudo mkdir /mnt/disk_mount_data
   

4. Mount temporarily:

    sudo mount /dev/sdb /mnt/disk_mount_data
   

5. Mount permanently (add to /etc/fstab):

    # Get UUID
    sudo blkid /dev/sdb
    # Add to fstab
    echo "UUID=e0ae19c8-abce /mnt/disk_mount_data ext4 defaults 0 0" | sudo tee -a /etc/fstab
   

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Key Scenarios Compared

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When to Use Direct Mounting vs. LVM

Use Direct Mounting (No LVM) When:

• You need simplicity (single disk, no scaling)

• Working with boot partitions

• Using removable media (USB drives)

• Storage needs are static

Choose LVM When You Need:

• Flexibility: Growing/shrinking partitions

• Scalability: Combining multiple physical disks

• Advanced Features: Snapshots, thin provisioning

• Live Operations: Resizing without unmounting

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Using a Loop Device Locally (For Practice)

If you're practicing on a local machine without additional disks, you can create a loop device:

What is a Loop Device?

A loop device is a virtual block device that maps a regular file to a "virtual disk." It allows files to behave like physical disks, letting you:

• Format files as disk images

• Mount files as filesystems

• Test partitioning schemes

• Create encrypted containers

Real-World Analogy:
Think of it as a virtual CD/DVD drive that uses an ISO file instead of physical media.

Create a Loop Device

1. Create a file to act as a virtual disk:

    sudo dd if=/dev/zero of=/storagefile bs=1M count=1024
   

2. Associate it with a loop device:

    sudo losetup -fP /storagefile  # -f: Find next available loop device 
    # Output: Now using /dev/loop0
   

3. Verify Loop Devices:

    losetup -a
    # Output: /dev/loop0: []: (/storagefile)
   

4. Follow the same steps to create a Physical Volume, Volume Group, and Logical Volume on this loop device.

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Working with Disk Partitions on Loop Devices

Case 1: Using the Entire Disk (No Partitions)

Good for: Simple use cases (single filesystem).
Workflow:

# Mount directly
sudo mount /dev/loop0 /mnt

Case 2: Creating Partitions

Good for: Simulating multi-partition disks (e.g., testing boot/root setups).
Workflow:

1. Create partitions on the loop device:

    sudo fdisk /dev/loop0
   

   • Press n to create new partitions (e.g., 500MB and 500MB).

   • Press w to save changes.

2. Reload partition table:

    sudo partprobe /dev/loop0
   

3. Format partitions:

    sudo mkfs.ext4 /dev/loop0p1  # First partition
    sudo mkfs.xfs /dev/loop0p2   # Second partition
   

4. Mount partitions:

    sudo mount /dev/loop0p1 /mnt/part1
    sudo mount /dev/loop0p2 /mnt/part2
   

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Unmounting: Safe Disconnection

Mounting and unmounting do not alter data on the storage medium. They only manage access to the data.

• Data persistence: Files remain intact unless explicitly modified or deleted.

• No formatting required: Mounting a pre-formatted device doesn’t erase it.

• Metadata preservation: Ownership, permissions, and timestamps stay unchanged.

Example:

sudo umount /mnt/usb

Exception: Data loss can occur if:

• You format the device (e.g., mkfs.ext4).

• You unplug hardware without unmounting (risking partial writes).

• There’s physical damage or filesystem corruption.

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Dynamic Storage Management: When Size Does Matter

Common Use Cases for LVM Operations

Useful Commands Cheat Sheet

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Pro Tips and Pitfalls to Avoid

✅ Best Practices

• Always back up data before resizing operations

• Use -r flag with lvextend to resize filesystem automatically

lvextend -r -L +5G /dev/vg_data/lv_data

• Monitor VG free space with vgs

❌ Common Mistakes:

• Forgetting to resize filesystem after LV extension

• Assuming all space is available (check VG free space first)

• Using LVM on flash drives (can reduce lifespan)

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Conclusion: Embrace Storage Flexibility

LVM transforms storage management from a rigid chore into a dynamic, flexible process. Whether you're:

• Scaling cloud storage in AWS

• Optimizing local disk or drives

• Creating development environments

The power to resize, reshape, and reconfigure storage on-demand is an essential skill for any Linux professional.

I hope this blog helps you get started and feel confident in managing Linux storage. Happy learning!