How filesystem snapshots work (Copy on Write)

Before Snapshot

	Allocation Table
		Disk Blocks

Create Snapshot

	Original Allocation Table
		Disk Blocks
	Snapshot Allocation Table

Application write to block 4

	Original Allocation Table
		Original Disk Blocks
		Copied Disk Blocks
	Snapshot Allocation Table

How filesystem snapshots work (Redirect on Write)

Before Snapshot

	Allocation Table
		Disk Blocks

Create Snapshot

	Original Allocation Table
		Disk Blocks
	Snapshot Allocation Table

Application write to block 4

	Original Allocation Table
		Newly Allocated Disk Blocks
		Original Disk Blocks
	Snapshot Allocation Table