LVM Management

LVM (Logical Volume Manager) is a powerful disk management tool in Linux. It adds an abstraction layer between physical disks and filesystems, making storage allocation and resizing much more flexible.

LVM Core Concepts

LVM consists of three layers:

Layer	Abbreviation	Description
Physical Volume	PV (Physical Volume)	The underlying disk or partition; the foundational building block of LVM
Volume Group	VG (Volume Group)	A storage pool composed of one or more PVs
Logical Volume	LV (Logical Volume)	A logical partition allocated from a VG; can be formatted and mounted

The layer relationships are as follows:

Disk/Partition  -->  PV  -->  VG  -->  LV  -->  Filesystem
/dev/sdb1       -->  PV1 -+
                          +-->  vg_data  -->  lv_app    -->  /app
/dev/sdc1       -->  PV2 -+              -->  lv_backup -->  /backup

Tip

The key advantages of LVM are: logical volumes can be extended without downtime, logical volumes can span multiple physical disks, and snapshot functionality is supported.

Installing LVM Tools

Most Enterprise Linux distributions come with LVM pre-installed. If it is not installed:

sudo dnf install lvm2 -y

Creating Physical Volumes (PV)

Physical volumes are the foundation layer of LVM. Disks or partitions must first be initialized as PVs.

Preparing Disk Partitions

First, use fdisk or gdisk to create a partition and set its type to 8e (Linux LVM):

sudo fdisk /dev/sdb
# n -> p -> 1 -> Enter -> Enter -> t -> 8e -> w
sudo partprobe /dev/sdb

Initializing Physical Volumes

sudo pvcreate /dev/sdb1
sudo pvcreate /dev/sdc1

You can also create a PV directly on an entire disk (no prior partitioning needed):

sudo pvcreate /dev/sdd

Viewing Physical Volume Information

# Brief listing
sudo pvs

# Detailed information
sudo pvdisplay /dev/sdb1

Creating Volume Groups (VG)

Volume groups pool multiple PVs into a unified storage pool.

Creating a Volume Group

sudo vgcreate vg_data /dev/sdb1 /dev/sdc1

Viewing Volume Group Information

# Brief listing
sudo vgs

# Detailed information
sudo vgdisplay vg_data

Extending a Volume Group

When new disks are added later, you can add new PVs to an existing VG:

sudo pvcreate /dev/sdd1
sudo vgextend vg_data /dev/sdd1

Removing a Physical Volume from a Volume Group

# First migrate data to other PVs
sudo pvmove /dev/sdc1

# Then remove from the VG
sudo vgreduce vg_data /dev/sdc1

Creating Logical Volumes (LV)

Logical volumes are usable storage space carved out from a volume group that can be formatted and mounted.

Creating with a Specified Size

sudo lvcreate -L 50G -n lv_app vg_data

Creating with a Percentage of Remaining VG Space

# Use 100% of the remaining VG space
sudo lvcreate -l 100%FREE -n lv_backup vg_data

Viewing Logical Volume Information

# Brief listing
sudo lvs

# Detailed information
sudo lvdisplay /dev/vg_data/lv_app

Formatting and Mounting a Logical Volume

# Format as XFS
sudo mkfs.xfs /dev/vg_data/lv_app

# Create a mount point and mount
sudo mkdir -p /app
sudo mount /dev/vg_data/lv_app /app

# Verify
df -hT /app

Configuring fstab for Auto-Mounting

# Get the LV's UUID (you can also use the LV path directly)
sudo blkid /dev/vg_data/lv_app

# Edit fstab
echo '/dev/vg_data/lv_app  /app  xfs  defaults  0  0' | sudo tee -a /etc/fstab

Note

The device path for an LV has two equivalent forms: /dev/vg_data/lv_app or /dev/mapper/vg_data-lv_app. Both point to the same device.

Extending Logical Volumes

One of LVM’s most powerful features is online logical volume extension.

Extending an LV and Its Filesystem Simultaneously

The -r flag extends the filesystem automatically along with the LV:

# Add 20G of space
sudo lvextend -r -L +20G /dev/vg_data/lv_app

Extending to a Specific Size

# Extend the LV to 100G
sudo lvextend -r -L 100G /dev/vg_data/lv_app

Extending Using All Remaining Space

sudo lvextend -r -l +100%FREE /dev/vg_data/lv_app

Step-by-Step Extension (manually extending the filesystem)

If you do not use the -r flag, you need to extend the filesystem manually:

# Step 1: Extend the LV
sudo lvextend -L +20G /dev/vg_data/lv_app

# Step 2: Extend the filesystem
# For XFS filesystems
sudo xfs_growfs /app

# For EXT4 filesystems
sudo resize2fs /dev/vg_data/lv_app

Tip

It is recommended to use lvextend -r, which automatically detects the filesystem type and calls the appropriate extension command, saving you from manual steps.

Viewing LVM Status: pvs/vgs/lvs

These three commands are the most commonly used LVM status queries in day-to-day operations.

pvs - Physical Volume Summary

sudo pvs

PV         VG      Fmt  Attr PSize   PFree
/dev/sdb1  vg_data lvm2 a--  <50.00g  0
/dev/sdc1  vg_data lvm2 a--  <50.00g  30.00g

vgs - Volume Group Summary

sudo vgs

VG      #PV #LV #SN Attr   VSize  VFree
vg_data   2   2   0 wz--n- 99.99g 30.00g

lvs - Logical Volume Summary

sudo lvs

LV        VG      Attr       LSize  Pool Origin Data%  Meta%
lv_app    vg_data -wi-ao---- 50.00g
lv_backup vg_data -wi-ao---- 19.99g

Customizing Output Fields

# Show LV name, size, volume group, and device path
sudo lvs -o lv_name,lv_size,vg_name,lv_path

LVM Snapshots

LVM snapshots create a read-only or read-write copy of a logical volume at a specific point in time. They are commonly used for backups and testing.

Caution

Snapshots consume available space in the volume group. Once the snapshot space is exhausted, the snapshot becomes unusable. Allocate snapshot size appropriately based on the expected data change volume.

Creating a Snapshot

# Create a 10G snapshot of lv_app
sudo lvcreate -s -L 10G -n lv_app_snap /dev/vg_data/lv_app

Parameter descriptions:

• -s: Create a snapshot
• -L 10G: Snapshot space size (for storing changed data)
• -n lv_app_snap: Snapshot name

Viewing Snapshot Status

sudo lvs

Snapshot volumes display the Origin (source volume) and Data% (percentage of snapshot space used).

Mounting a Snapshot (read-only access to historical data)

sudo mkdir -p /mnt/snap
sudo mount -o ro /dev/vg_data/lv_app_snap /mnt/snap

Restoring Data from a Snapshot

You can copy needed files from the snapshot:

sudo cp /mnt/snap/important-file.conf /app/important-file.conf

Or merge the snapshot to roll back the entire logical volume:

# First unmount the source volume and the snapshot
sudo umount /app
sudo umount /mnt/snap

# Merge the snapshot (roll back to the state at snapshot time)
sudo lvconvert --merge /dev/vg_data/lv_app_snap

# Remount
sudo mount /dev/vg_data/lv_app /app

Deleting a Snapshot

sudo umount /mnt/snap
sudo lvremove /dev/vg_data/lv_app_snap

Removing LVM Resources

When removing LVM resources, you must work in order: LV -> VG -> PV.

1. Unmount and remove the logical volume:

   sudo umount /app
   sudo lvremove /dev/vg_data/lv_app

2. Remove the volume group:

   sudo vgremove vg_data

3. Remove the physical volumes:

   sudo pvremove /dev/sdb1 /dev/sdc1

Hands-On: From Disk to LVM Mount

The following demonstrates the complete process of setting up LVM storage using two new disks, /dev/sdb and /dev/sdc.

1. Create partitions on both disks:

   sudo parted /dev/sdb mklabel gpt
   sudo parted /dev/sdb mkpart primary 0% 100%
   sudo parted /dev/sdc mklabel gpt
   sudo parted /dev/sdc mkpart primary 0% 100%
   sudo partprobe

2. Create physical volumes:

   sudo pvcreate /dev/sdb1 /dev/sdc1
   sudo pvs

3. Create a volume group:

   sudo vgcreate vg_data /dev/sdb1 /dev/sdc1
   sudo vgs

4. Create logical volumes:

   sudo lvcreate -L 80G -n lv_app vg_data
   sudo lvcreate -l 100%FREE -n lv_logs vg_data
   sudo lvs

5. Format and mount:

   sudo mkfs.xfs /dev/vg_data/lv_app
   sudo mkfs.xfs /dev/vg_data/lv_logs
   sudo mkdir -p /app /var/applogs
   sudo mount /dev/vg_data/lv_app /app
   sudo mount /dev/vg_data/lv_logs /var/applogs

6. Configure auto-mounting at boot:

   sudo cp /etc/fstab /etc/fstab.bak
   cat <<EOF | sudo tee -a /etc/fstab
   /dev/vg_data/lv_app   /app          xfs  defaults  0  0
   /dev/vg_data/lv_logs  /var/applogs  xfs  defaults  0  0
   EOF
   sudo mount -a

7. Verify the results:

   df -hT /app /var/applogs
   sudo pvs && sudo vgs && sudo lvs

The flexibility of LVM makes it the preferred solution for managing storage in Enterprise Linux environments. Mastering PV, VG, and LV operations along with online extension and snapshot capabilities will greatly improve storage management efficiency.