4.3 Logical Volume Management (LVM)

LVM allows you to abstract physical storage. You can combine multiple disks into one pool and resize volumes on the fly.

Concepts

graph TD
    Disk1[Physical Disk 1 /dev/sdb] --> PV1[Physical Volume]
    Disk2[Physical Disk 2 /dev/sdc] --> PV2[Physical Volume]
    PV1 --> VG[Volume Group 'my_vg']
    PV2 --> VG
    VG --> LV1[Logical Volume 'db_vol']
    VG --> LV2[Logical Volume 'web_vol']
    LV1 --> FS1[Ext4 Filesystem]
    LV2 --> FS2[XFS Filesystem]

Implementation Steps

1. Physical Volumes (PV)

Mark the raw disks for LVM use.

sudo pvcreate /dev/sdb /dev/sdc

2. Volume Group (VG)

Create a pool called data_vg.

sudo vgcreate data_vg /dev/sdb /dev/sdc

3. Logical Volume (LV)

Carve out a chunk.

# Create a 10GB volume named 'backups'
sudo lvcreate -n backups -L 10G data_vg

It is accessed at /dev/data_vg/backups.

4. Format and Mount

Treat it like a normal partition.

sudo mkfs.ext4 /dev/data_vg/backups
sudo mount /dev/data_vg/backups /mnt/backups

Resizing (The magic of LVM)

If you run out of space in backups, and data_vg has free space:

# Extend the LV and the Filesystem in one go (-r)
sudo lvextend -L +5G -r /dev/data_vg/backups