Logical Volume Management

Objective

Create and manage LVM physical volumes, volume groups, and logical volumes. Extend an online filesystem without downtime.

Tools & Technologies

pvcreate
vgcreate
lvcreate
lvextend
resize2fs
pvdisplay

Key Commands

pvcreate /dev/sdb

vgcreate vg0 /dev/sdb

lvcreate -L 10G -n lv_data vg0

lvextend -L +5G /dev/vg0/lv_data

resize2fs /dev/vg0/lv_data

Architecture Overview

graph LR subgraph Physical Layer PV1[/dev/sdb\nPV] PV2[/dev/sdc\nPV] end subgraph Logical Layer PV1 --> VG[vg0\nVolume Group\n30GB pool] PV2 --> VG VG --> LV1[lv_root\n15GB] VG --> LV2[lv_data\n10GB] VG --> FREE[5GB free] end subgraph Filesystems LV1 --> FS1[ext4\n/] LV2 --> FS2[ext4\n/data] end style VG fill:#1a1a2e,stroke:#00d4ff,color:#e0e0e0

Step-by-Step Process

Create Physical Volume

Initialize a disk or partition as an LVM physical volume.

# Initialize disk as PV
sudo pvcreate /dev/sdb
sudo pvdisplay /dev/sdb
sudo pvs   # brief summary

Create Volume Group

A volume group pools one or more PVs into a storage pool.

sudo vgcreate vg0 /dev/sdb
# Add second disk to existing VG
sudo vgextend vg0 /dev/sdc
sudo vgdisplay vg0
sudo vgs

Create and Use Logical Volumes

Create logical volumes from the VG pool, format them, and mount.

sudo lvcreate -L 10G -n lv_data vg0
sudo mkfs.ext4 /dev/vg0/lv_data
sudo mkdir /data
sudo mount /dev/vg0/lv_data /data

# Persist in fstab
echo '/dev/vg0/lv_data /data ext4 defaults 0 2' | sudo tee -a /etc/fstab

Extend Online (Zero Downtime)

Grow a filesystem while it is mounted and in use.

# Extend LV by 5GB
sudo lvextend -L +5G /dev/vg0/lv_data
# Grow filesystem to fill LV
sudo resize2fs /dev/vg0/lv_data  # ext4
# For XFS:
sudo xfs_growfs /data

# Verify
df -h /data

Challenges & Solutions

resize2fs only works on ext2/3/4 — XFS uses xfs_growfs
Shrinking LVM requires unmounting and offline resize2fs — risky without backup

Key Takeaways

LVM snapshots use copy-on-write — perfect for pre-maintenance backups
PE size determines minimum allocation granularity