Comprehensive LVM Tutorial with Examples

Introduction to LVM

Logical Volume Manager (LVM) is a storage management solution that provides flexibility in managing disk storage. It allows dynamic resizing, combining multiple disks, and creating snapshots, among other features.

LVM Components:

Physical Volume (PV) – A physical disk or partition initialized for LVM.
Volume Group (VG) – A pool of storage created from one or more PVs.
Logical Volume (LV) – A partition-like entity created from a VG.
File System – The file system (ext4, XFS, etc.) created on an LV for data storage.

Setting Up LVM

1. Installing LVM (If Not Already Installed)

sudo apt install lvm2      # Debian/Ubuntu
sudo yum install lvm2      # RHEL/CentOS
sudo dnf install lvm2      # Fedora

2. Creating Physical Volumes (PVs)

Convert a disk or partition into an LVM Physical Volume.

sudo pvcreate /dev/sdb /dev/sdc

Check PV status:

sudo pvs

3. Creating a Volume Group (VG)

Create a Volume Group named vg_data from two disks:

sudo vgcreate vg_data /dev/sdb /dev/sdc

Verify VG status:

sudo vgs

4. Creating a Logical Volume (LV)

Create a Logical Volume of 50GB from vg_data:

sudo lvcreate -L 50G -n lv_storage vg_data

Check LV status:

sudo lvs

5. Formatting and Mounting the Logical Volume

Format the LV with the ext4 file system:

sudo mkfs.ext4 /dev/vg_data/lv_storage

Create a mount point and mount the LV:

sudo mkdir /mnt/storage
sudo mount /dev/vg_data/lv_storage /mnt/storage

To mount it automatically at boot, add it to /etc/fstab:

echo "/dev/vg_data/lv_storage /mnt/storage ext4 defaults 0 2" | sudo tee -a /etc/fstab

Managing LVM

6. Expanding a Logical Volume (LV) When Running Out of Space

If lv_storage is full, increase its size:

sudo lvextend -L +20G /dev/vg_data/lv_storage   # Add 20GB
sudo resize2fs /dev/vg_data/lv_storage         # Resize ext4 filesystem

For XFS file systems:

sudo xfs_growfs /mnt/storage

7. Adding a New Disk to Expand the Volume Group

If you need more space, add a new disk (/dev/sdd) to vg_data:

sudo pvcreate /dev/sdd
sudo vgextend vg_data /dev/sdd

Check available space:

sudo vgs

8. Reducing the Size of a Logical Volume

Unmount the LV first:

sudo umount /mnt/storage

Resize the filesystem (for ext4):

sudo e2fsck -f /dev/vg_data/lv_storage
sudo resize2fs /dev/vg_data/lv_storage 30G

Reduce LV size:

sudo lvreduce -L 30G /dev/vg_data/lv_storage

Remount the LV:

sudo mount /dev/vg_data/lv_storage /mnt/storage

9. Removing a Logical Volume

Unmount the LV:

sudo umount /mnt/storage

Remove LV:

sudo lvremove /dev/vg_data/lv_storage

10. Removing a Physical Volume from a Volume Group

To remove /dev/sdd from vg_data, first, move data:

sudo pvmove /dev/sdd

Then, remove it:

sudo vgreduce vg_data /dev/sdd
sudo pvremove /dev/sdd

11. Splitting a Volume Group

If you need to split vg_data into two groups:

sudo vgsplit vg_data vg_backup /dev/sdd

12. Merging Two Volume Groups

Merge vg_backup into vg_data:

sudo vgmerge vg_data vg_backup

Handling Out-of-Space Situations

Scenario 1: Expanding an LV Using Free VG Space

sudo lvextend -L +10G /dev/vg_data/lv_storage
sudo resize2fs /dev/vg_data/lv_storage

Scenario 2: Adding a New Disk to VG and Expanding LV

sudo pvcreate /dev/sde
sudo vgextend vg_data /dev/sde
sudo lvextend -L +20G /dev/vg_data/lv_storage
sudo resize2fs /dev/vg_data/lv_storage

Scenario 3: Moving Data and Reconfiguring LVM

If the VG is full and you need to migrate data:

sudo pvmove /dev/sdb /dev/sdf  # Move data to a new disk
sudo vgreduce vg_data /dev/sdb  # Remove old disk

Conclusion

LVM provides flexible storage management, allowing resizing, adding/removing disks, and efficiently handling disk space. Regular monitoring using lvdisplay, vgdisplay, and pvs helps in managing storage effectively.

Recommended Practices:

Always backup data before resizing or removing LVs.
Use pvmove before removing a disk from a VG.
Monitor disk usage with df -h and lvs.

By mastering LVM, you gain powerful control over disk storage without downtime.