https://drive.google.com/file/d/1mF8qYj522jmvLour6D7_Hrl3u1_0tLkM/view?usp=sharing

1. Understanding LVM Snapshots

Purpose

• Point-in-time backup of a Logical Volume (LV).
• Allows you to:
  • Safely backup data while system is running
  • Roll back to a previous state after accidental deletion/corruption
• Copy-on-write (COW): Only changed blocks are stored in snapshot.

⚠️ Critical Notes:

• Snapshot size must accommodate expected changes during its lifetime.
• If snapshot fills up → becomes invalid (data loss risk!).
• Cannot merge while origin LV is mounted (in older RHEL versions).

2. Lab Setup: Create LVM with Snapshot

Prepare Disk and Partitions

# Add 10GB disk (e.g., /dev/sdb)
sudo fdisk /dev/sdb
# Create two partitions:
#   n → p → 1 → [Enter] → +5G → t → 8e
#   n → p → 2 → [Enter] → +5G → t → 8e
#   w
sudo partprobe
lsblk    # Verify sdb1, sdb2

Create LVM

# Create PV and VG
sudo pvcreate /dev/sdb1
sudo vgcreate system /dev/sdb1

# Create LV (3GB)
sudo lvcreate -L 3G -n data system
sudo mkfs.ext4 /dev/system/data

# Mount and add test data
sudo mkdir /data
sudo mount /dev/system/data /data
cd /data
touch test{1..5}
cal > cal.txt
mkdir aa bb cc
cd
du -sh /data    # Note size (e.g., 20K)

3. Create and Use Snapshot

Create Snapshot

# Create 1GB snapshot (name: snap_data)
sudo lvcreate -L 1G -s -n snap_data /dev/system/data
sudo lvs    # Verify: snap_data (snapshot), data (origin)

💡 Snapshot Size Rule:

Allocate 20-30% of origin LV size for moderate changes.

For 3GB LV → 1GB snapshot is reasonable for short-term use.

Simulate Data Loss