Creating and Managing LVM

Creating and Managing LVM

LVM (Logical Volume Manager) adds an abstraction layer between physical storage and file systems. Instead of formatting partitions directly, you create a pool of storage (Volume Group) from one or more disks, then carve out Logical Volumes from that pool. The key advantage: you can resize, move, and snapshot volumes while they are online. This is why Ubuntu uses LVM by default in the server installer.

LVM architecture

Physical level:
  /dev/sdb        /dev/sdc
      |               |
  pvcreate    pvcreate
      |               |
      ↓               ↓
  Physical Volumes (PV): /dev/sdb, /dev/sdc
              |
          vgcreate vg_data /dev/sdb /dev/sdc
              |
              ↓
  Volume Group (VG): vg_data  [total: 1 TB]
          /           |                lvcreate    lvcreate    lvcreate
          |           |           |
          ↓           ↓           ↓
  Logical Volumes (LV):
    /dev/vg_data/mysql   [200 GB]
    /dev/vg_data/logs    [300 GB]
    /dev/vg_data/backup  [500 GB]
          |
      mkfs.ext4 or mkfs.xfs
          |
      mount /dev/vg_data/mysql /var/lib/mysql

Creating LVM from scratch

# Step 1: Install LVM tools
sudo apt install -y lvm2

# Step 2: Prepare disks — partition them with type "Linux LVM"
# Either: use whole disk directly as PV (simpler, common for dedicated storage)
# Or: partition first and use the partition as PV (required for mixed-use disks)

# Use whole disk as PV:
sudo pvcreate /dev/sdb /dev/sdc

# Or use a partition:
# sudo fdisk /dev/sdb → n → Enter → Enter → Enter → t → 30 (Linux LVM) → w
# sudo pvcreate /dev/sdb1

# Step 3: Create a Volume Group from the physical volumes
sudo vgcreate vg_data /dev/sdb /dev/sdc

# Verify
sudo pvs     # Show physical volumes
sudo vgs     # Show volume groups

pvs and vgs output

  PV         VG      Fmt  Attr PSize   PFree
  /dev/sdb   vg_data lvm2 a--  500.00g 500.00g
  /dev/sdc   vg_data lvm2 a--  500.00g 500.00g

  VG      #PV #LV #SN Attr   VSize    VFree
  vg_data   2   0   0 wz--n- 999.99g  999.99g

Creating logical volumes

# Create a logical volume with a specific size
sudo lvcreate -n mysql -L 200G vg_data

# Create a logical volume using percentage of free space
sudo lvcreate -n logs -l 30%FREE vg_data

# Create a logical volume using ALL remaining free space
sudo lvcreate -n backup -l 100%FREE vg_data

# Format and mount the logical volume (accessed via /dev/VG/LV or /dev/mapper/VG-LV)
sudo mkfs.xfs /dev/vg_data/mysql
sudo mkdir -p /var/lib/mysql
sudo mount /dev/vg_data/mysql /var/lib/mysql

# Add to /etc/fstab (use /dev/mapper name for reliability)
echo "/dev/mapper/vg_data-mysql  /var/lib/mysql  xfs  defaults,noatime  0  2" | sudo tee -a /etc/fstab

# Verify
sudo lvs    # Show logical volumes
df -h /var/lib/mysql

Managing volume groups

# Add a new physical disk to an existing volume group (expand the pool)
sudo pvcreate /dev/sdd
sudo vgextend vg_data /dev/sdd
sudo vgs    # VSize should now be larger

# Remove a disk from a volume group (move data off it first)
sudo pvmove /dev/sdb    # Moves all data from sdb to other PVs in VG (slow)
sudo vgreduce vg_data /dev/sdb
sudo pvremove /dev/sdb

# Rename a volume group
sudo vgrename vg_data vg_production

# Delete a volume group (WARNING: destroys all LVs and data)
# sudo lvremove /dev/vg_data/*
# sudo vgremove vg_data
# sudo pvremove /dev/sdb /dev/sdc

LVM display commands

# Quick overview of all LVM resources
sudo pvs     # Physical volumes: PV name, VG, size, free
sudo vgs     # Volume groups: name, PV count, LV count, size, free
sudo lvs     # Logical volumes: name, VG, size, attributes

# Detailed info about a specific object
sudo pvdisplay /dev/sdb
sudo vgdisplay vg_data
sudo lvdisplay /dev/vg_data/mysql

# Show LVM configuration for all objects
sudo lvscan    # List all LVs with active state

Conclusion

LVM is worth setting up whenever you need flexibility in storage management. The setup order is always: pvcreate on disks, vgcreate to pool them, lvcreate to carve out volumes, mkfs to format, mount to access. Expanding storage later is straightforward: add a disk with pvcreate + vgextend, then grow the LV with lvextend + resize2fs (or xfs_growfs for XFS). This is the standard storage management pattern for Ubuntu servers.