🐧 Linux LVM Complete Guide: PV / VG / LV Expansion, Reduction & Online Filesystem Resize

🐧 Linux LVM Complete Guide: PV / VG / LV Expansion, Reduction & Online Filesystem Resize

Running out of space on /var, /data, or your virtual machine disk is one of the most common storage issues in Linux servers. Without LVM (Logical Volume Manager), resizing partitions can be extremely painful. This guide explains LVM clearly — concepts → creation → expansion → reduction → common errors — with full examples for EXT4 and XFS online resize.

1. Why LVM? Traditional Partitioning vs LVM

Traditional partitioning uses fixed sizes created by fdisk or parted:

/dev/sda1 → /boot
/dev/sda2 → /
/dev/sda3 → /var
/dev/sda4 → /home

Disadvantages:

• Resizing later is painful or impossible.
• Adding a new disk cannot extend an existing mount point like /var or /data.

LVM treats storage like modular blocks:

• PV (Physical Volume): physical disks or partitions (e.g., /dev/sda2, /dev/sdb)
• VG (Volume Group): a capacity pool combining multiple PVs
• LV (Logical Volume): logical partitions carved from a VG

📦 Architecture Overview

Traditional:

/dev/sda
 ├─ /dev/sda1 → /
 ├─ /dev/sda2 → /var
 └─ /dev/sda3 → /home

LVM:

/dev/sda2   /dev/sdb
   │           │
   └── PVs → VG (vg_data)
               ├── LV: lv_var  → /var
               ├── LV: lv_home → /home
               └── LV: lv_data → /data

2. LVM Structure Overview: PV → VG → LV

Goal:
/dev/vg_main/lv_root → /
/dev/vg_main/lv_var  → /var
/dev/vg_main/lv_data → /data

/dev/sda2     /dev/sdb
    │            │
    └── PV0      └── PV1
           │
           └───── VG: vg_main
                    ├── LV: lv_root → /
                    ├── LV: lv_var  → /var
                    └── LV: lv_data → /data

3. Creating LVM from Scratch

1️⃣ Create partition (optional)

# Using whole disk:
sudo pvcreate /dev/sdb

# Using a partition:
sudo fdisk /dev/sdb   # create /dev/sdb1 type 8e
sudo pvcreate /dev/sdb1

2️⃣ Create PV, VG, LV

sudo pvcreate /dev/sda2
sudo pvcreate /dev/sdb1

sudo vgcreate vg_main /dev/sda2
sudo vgextend vg_main /dev/sdb1

sudo lvcreate -L 20G -n lv_root vg_main
sudo lvcreate -L 50G -n lv_var  vg_main
sudo lvcreate -L 100G -n lv_data vg_main

3️⃣ Format & mount

sudo mkfs.ext4 /dev/vg_main/lv_var
sudo mkfs.ext4 /dev/vg_main/lv_data

sudo mount /dev/vg_main/lv_var /var
sudo mount /dev/vg_main/lv_data /data

/dev/vg_main/lv_var  /var  ext4  defaults 0 2
/dev/vg_main/lv_data /data ext4  defaults 0 2

4. Online LVM Expansion (EXT4 & XFS)

Step 1: Check current state

df -h
lsblk
sudo vgs
sudo lvs

Step 2: Add disk and extend VG

sudo pvcreate /dev/sdc
sudo vgextend vg_main /dev/sdc
sudo vgs

Step 3: Extend LV (no downtime)

# Add 100G
sudo lvextend -L +100G /dev/vg_main/lv_data

# or consume all free space
sudo lvextend -l +100%FREE /dev/vg_main/lv_data

Step 4: Online filesystem expand

EXT4:

sudo resize2fs /dev/vg_main/lv_data

XFS:

sudo xfs_growfs /data

5. LVM Reduction (Dangerous!)

• XFS cannot shrink
• Safer: create a new LV and rsync to migrate
• EXT4 can shrink but only offline

EXT4 shrinking safe procedure

sudo systemctl stop nginx
sudo umount /data
sudo e2fsck -f /dev/vg_main/lv_data
sudo resize2fs /dev/vg_main/lv_data 200G
sudo lvreduce -L 200G /dev/vg_main/lv_data
sudo mount /data
df -h /data

6. Common Errors & Troubleshooting

❗ device is busy

umount: /data: target is busy.

sudo lsof +f -- /data
sudo fuser -vm /data

❗ VG has no free space

sudo vgs
sudo pvs

❗ lvextend done but df -h unchanged

# EXT4
sudo resize2fs /dev/vg_main/lv_data

# XFS
sudo xfs_growfs /data

Proxmox VM expansion scenario

sudo pvresize /dev/sda2
sudo lvextend -L +50G /dev/vg_main/lv_data
sudo xfs_growfs /data

7. LVM Quick Command Sheet

pvs / vgs / lvs  → overview
pvcreate          → create PV
vgcreate          → create VG
vgextend          → add PV to VG
lvcreate          → create LV
lvextend          → expand LV
resize2fs/xfs_growfs → grow filesystem
lvreduce + resize2fs → shrink EXT4 only

Conclusion

LVM gives Linux servers true flexibility. Once you practice the workflow — PV → VG → LV → filesystem resize — disk management becomes predictable and risk-free. This is especially essential for Proxmox, database servers, logging nodes, and any fast-growing storage environment.

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• 🐧 Linux Filesystem Comparison: EXT4, XFS, Btrfs, ZFS
• 🐧 Linux systemd Deep Dive
• 🐧 Linux Nginx Reverse Proxy & Load Balancing Guide

— WWFandy・Linux LVM Guide (English Edition)