lvm Command Linux: Complete Guide to Logical Volume Manager Operations

The Logical Volume Manager (LVM) is a powerful disk management tool in Linux that provides flexible storage management by abstracting physical storage devices into logical volumes. Unlike traditional partitioning, LVM allows dynamic resizing, snapshotting, and advanced storage operations without downtime.

What is LVM and Why Use It?

LVM creates a layer of abstraction between your operating system and physical storage devices. It combines multiple physical volumes (PVs) into volume groups (VGs), which are then divided into logical volumes (LVs). This approach offers several advantages:

• Dynamic Resizing: Expand or shrink volumes without unmounting
• Snapshots: Create point-in-time copies for backups
• Storage Pooling: Combine multiple drives into single logical units
• Striping and Mirroring: Improve performance and redundancy
• Easy Migration: Move data between physical devices seamlessly

LVM Architecture Overview

Understanding LVM’s three-tier architecture is crucial for effective management:

1. Physical Volume (PV): Raw storage devices or partitions
2. Volume Group (VG): Collection of physical volumes
3. Logical Volume (LV): Virtual partitions created from volume groups

Essential LVM Commands

Physical Volume Management

Creating Physical Volumes

Before using storage devices with LVM, you must initialize them as physical volumes:

# Initialize a disk as physical volume
sudo pvcreate /dev/sdb1

# Initialize multiple disks
sudo pvcreate /dev/sdb1 /dev/sdc1 /dev/sdd1

Example Output:

Physical volume "/dev/sdb1" successfully created.
Physical volume "/dev/sdc1" successfully created.
Physical volume "/dev/sdd1" successfully created.

Viewing Physical Volume Information

# Display all physical volumes
sudo pvdisplay

# Show summary of physical volumes
sudo pvs

# Detailed scan of physical volumes
sudo pvscan

Sample pvdisplay Output:

--- Physical volume ---
PV Name               /dev/sdb1
VG Name               my_vg
PV Size               1.82 TiB / not usable 3.00 MiB
Allocatable           yes 
PE Size               4.00 MiB
Total PE              476932
Free PE               238466
Allocated PE          238466
PV UUID               k5H7Vm-pQP6-Af6D-5i0B-85CQ-cVF6-MlOJ21

Volume Group Management

Creating Volume Groups

Volume groups combine one or more physical volumes into a storage pool:

# Create volume group with single PV
sudo vgcreate my_vg /dev/sdb1

# Create volume group with multiple PVs
sudo vgcreate my_vg /dev/sdb1 /dev/sdc1

# Create VG with specific extent size
sudo vgcreate -s 8M my_vg /dev/sdb1

Extending Volume Groups

# Add physical volume to existing VG
sudo vgextend my_vg /dev/sdd1

# Remove PV from VG (must be empty)
sudo vgreduce my_vg /dev/sdd1

Volume Group Information

# Display detailed VG information
sudo vgdisplay my_vg

# Show VG summary
sudo vgs

# Scan for volume groups
sudo vgscan

Sample vgs Output:

VG    #PV #LV #SN Attr   VSize   VFree  
my_vg   2   3   0 wz--n- <1.82t <930.00g

Logical Volume Management

Creating Logical Volumes

Logical volumes are the final layer where you create filesystems:

# Create LV with specific size
sudo lvcreate -L 10G -n my_lv my_vg

# Create LV using percentage of VG
sudo lvcreate -l 50%VG -n data_lv my_vg

# Create LV using all free space
sudo lvcreate -l 100%FREE -n backup_lv my_vg

# Create striped LV for performance
sudo lvcreate -L 20G -i 2 -n striped_lv my_vg

Command Breakdown:

• -L: Size in bytes (K, M, G, T suffixes)
• -l: Size in logical extents or percentages
• -n: Name of the logical volume
• -i: Number of stripes

Logical Volume Information

# Display detailed LV information
sudo lvdisplay /dev/my_vg/my_lv

# Show LV summary
sudo lvs

# Scan for logical volumes
sudo lvscan

Sample lvs Output:

LV        VG    Attr       LSize   Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
my_lv     my_vg -wi-ao---- 10.00g                                                    
data_lv   my_vg -wi-a----- 465.63g                                                   
backup_lv my_vg -wi-a----- 465.63g

Advanced LVM Operations

Resizing Logical Volumes

One of LVM’s most powerful features is dynamic resizing:

Extending Logical Volumes

# Extend LV by 5GB
sudo lvextend -L +5G /dev/my_vg/my_lv

# Extend LV to 20GB total
sudo lvextend -L 20G /dev/my_vg/my_lv

# Extend and resize filesystem simultaneously
sudo lvextend -L +5G -r /dev/my_vg/my_lv

Shrinking Logical Volumes

⚠️ Warning: Always backup data before shrinking volumes. Shrinking can cause data loss if not done properly.

# First, unmount the filesystem
sudo umount /dev/my_vg/my_lv

# Check filesystem
sudo e2fsck -f /dev/my_vg/my_lv

# Shrink filesystem first
sudo resize2fs /dev/my_vg/my_lv 8G

# Then shrink the LV
sudo lvreduce -L 8G /dev/my_vg/my_lv

# Remount
sudo mount /dev/my_vg/my_lv /mnt/my_mount

LVM Snapshots

Snapshots create point-in-time copies of logical volumes, perfect for backups or testing:

# Create snapshot (10% of original LV size)
sudo lvcreate -L 2G -s -n my_lv_snapshot /dev/my_vg/my_lv

# Create snapshot with specific size
sudo lvcreate -L 5G -s -n backup_snapshot /dev/my_vg/data_lv

# Mount snapshot for backup
sudo mkdir /mnt/snapshot
sudo mount /dev/my_vg/my_lv_snapshot /mnt/snapshot

Managing Snapshots

# View snapshot information
sudo lvs -o +snap_percent

# Remove snapshot
sudo lvremove /dev/my_vg/my_lv_snapshot

# Merge snapshot back to origin
sudo lvconvert --merge /dev/my_vg/my_lv_snapshot

Complete LVM Setup Example

Here’s a comprehensive example showing the complete LVM setup process:

# Step 1: Prepare disks
sudo fdisk /dev/sdb
# Create partition and set type to 'Linux LVM' (8e)

# Step 2: Create physical volumes
sudo pvcreate /dev/sdb1 /dev/sdc1

# Step 3: Create volume group
sudo vgcreate production_vg /dev/sdb1 /dev/sdc1

# Step 4: Create logical volumes
sudo lvcreate -L 50G -n web_lv production_vg
sudo lvcreate -L 30G -n db_lv production_vg
sudo lvcreate -l 100%FREE -n logs_lv production_vg

# Step 5: Create filesystems
sudo mkfs.ext4 /dev/production_vg/web_lv
sudo mkfs.ext4 /dev/production_vg/db_lv
sudo mkfs.ext4 /dev/production_vg/logs_lv

# Step 6: Mount filesystems
sudo mkdir -p /var/www /var/lib/mysql /var/log/apps
sudo mount /dev/production_vg/web_lv /var/www
sudo mount /dev/production_vg/db_lv /var/lib/mysql
sudo mount /dev/production_vg/logs_lv /var/log/apps

LVM Troubleshooting

Common Issues and Solutions

LV Won’t Activate

# Manually activate logical volume
sudo lvchange -ay /dev/my_vg/my_lv

# Activate all LVs in VG
sudo vgchange -ay my_vg

# Check LVM configuration
sudo lvmdiskscan

Missing Physical Volume

# Display missing PVs
sudo vgdisplay -v my_vg

# Remove missing PV (if data is backed up)
sudo vgreduce --removemissing my_vg

# Force removal if necessary
sudo vgreduce --removemissing --force my_vg

Recovery Operations

# Backup LVM metadata
sudo vgcfgbackup

# Restore from backup
sudo vgcfgrestore my_vg

# Scan and rebuild cache
sudo pvscan --cache
sudo vgscan --mknodes

Performance Optimization

Striping for Performance

# Create striped LV across multiple PVs
sudo lvcreate -L 100G -i 3 -I 64k -n fast_lv my_vg

# Parameters:
# -i 3: Stripe across 3 devices
# -I 64k: 64KB stripe size

Monitoring LVM Performance

# Monitor I/O statistics
sudo iostat -x 1

# LVM-specific monitoring
sudo dmsetup info
sudo dmsetup status

Best Practices

Planning and Design

• Naming Convention: Use descriptive names for VGs and LVs
• Extent Size: Use larger extent sizes for better performance with large volumes
• Reserve Space: Keep 15-20% free space in VGs for snapshots and growth
• Backup Strategy: Regular LVM metadata backups are crucial

Monitoring Commands

# Check system-wide LVM status
sudo lvs -a -o +devices
sudo vgs -o +pv_count,lv_count
sudo pvs -o +pv_used,pv_free

# Monitor space usage
df -h /dev/mapper/*

Conclusion

LVM provides tremendous flexibility for Linux storage management. Its layered approach allows for dynamic operations that would be impossible with traditional partitioning. Key benefits include easy resizing, snapshot capabilities, and the ability to span multiple physical devices.

Start with simple configurations and gradually explore advanced features like striping, mirroring, and thin provisioning. Always maintain regular backups of both your data and LVM metadata to ensure quick recovery from any issues.

The commands covered in this guide form the foundation of LVM administration. Practice these operations in a test environment before implementing them in production systems, and always follow the principle of backing up critical data before making structural changes to your storage layout.