LVM snapshots use a copy-on-write (COW) mechanism rather than creating full copies of your data. Here's the technical breakdown:

# Original volume (100GB)
lvcreate -L 100G -n original_vol vg0

# Snapshot volume (10GB COW space)
lvcreate -s -L 10G -n snap_vol /dev/vg0/original_vol

The key components are:

• Original LV: Your base logical volume containing actual data
• Snapshot LV: A special volume storing only changed blocks
• COW Metadata: LVM tracks which blocks have been modified

Here's how to properly implement snapshots for a fileserver backup rotation:

# Create daily snapshot sequence
for day in {1..7}; do
  lvcreate -s -L 5G -n snap_day${day} /dev/fileserverLVM/primary
  mount /dev/fileserverLVM/snap_day${day} /mnt/backups/day${day}
done

# Weekly rotation (after 7 days)
lvremove -f /dev/fileserverLVM/snap_day1
lvcreate -s -L 5G -n snap_week1 /dev/fileserverLVM/primary

The critical aspect is monitoring COW space allocation. When this fills up, the snapshot becomes invalid:

# Check snapshot allocation (critical for automation)
lvs -o +snap_percent /dev/fileserverLVM/snap_day1

# Extend snapshot space if needed
lvextend -L +2G /dev/fileserverLVM/snap_day1

For more complex backup schemes, you can create snapshot chains while maintaining efficiency:

# Base snapshot
lvcreate -s -L 10G -n base_snap /dev/fileserverLVM/primary

# Differential snapshot (only tracks changes since base)
lvcreate -s -L 5G -n diff_snap /dev/fileserverLVM/base_snap

# When removing base snapshot, promote differential:
lvconvert --mergesnapshot /dev/fileserverLVM/base_snap

Snapshot operations affect I/O performance differently:

• Read-heavy workloads: Minimal impact (1-3% overhead)
• Write-heavy workloads: Up to 30% overhead during COW operations
• Metadata operations: Significant impact when maintaining many snapshots (>10)

For production systems, consider these optimizations:

# Use separate physical volume for COW data
pvcreate /dev/sdb1
vgextend fileserverLVM /dev/sdb1
lvcreate -s -L 20G -n perf_snap /dev/fileserverLVM/primary --cow /dev/sdb1

Let me clarify the snapshot mechanism in LVM (Logical Volume Manager) based on your understanding. You're partially correct, but there are some important technical nuances:

• Snapshots don't initially create full copies - they use copy-on-write (COW) technology
• The snapshot volume stores only changed blocks from the original volume
• When you create a snapshot, LVM allocates space just for tracking changes
• The original volume (called origin) and snapshots share unchanged data blocks

Here's how the process works in practice:

# Create original volume
lvcreate -L 100G -n origin_vol vg00

# Create snapshot (10GB space for tracking changes)
lvcreate -s -n snap1 -L 10G /dev/vg00/origin_vol

# After some changes, create second snapshot
lvcreate -s -n snap2 -L 10G /dev/vg00/origin_vol

Looking at your vgdisplay output showing only 524MB free space, you need to consider:

1. Snapshot space requirements depend on:
   • Change rate of your filesystem
   • Retention period
   • Snapshot frequency
2. When removing snapshots:

   lvremove /dev/vg00/snap1

   Subsequent snapshots will still reference the origin volume directly

For a fileserver backup system, consider this automated approach:

#!/bin/bash
# Daily snapshot rotation script
SNAP_PREFIX="daily_"
MAX_SNAPS=7

# Remove oldest snapshot if we've reached maximum
if [ $(lvs --noheadings -o lv_name | grep "^${SNAP_PREFIX}" | wc -l) -ge $MAX_SNAPS ]; then
   OLDEST=$(lvs --noheadings -o lv_name | grep "^${SNAP_PREFIX}" | sort | head -n 1)
   lvremove -f /dev/vg00/$OLDEST
fi

# Create new snapshot
TODAY=$(date +%Y%m%d)
lvcreate -s -n ${SNAP_PREFIX}${TODAY} -L 10G /dev/vg00/origin_vol

Important factors affecting snapshot performance:

For production systems, always test snapshot performance with your specific workload before deployment.