Determine if two files are identical

How would you determine whether two files are identical at scale? Describe a step-by-step approach covering: choice of hashing algorithms (e.g., MD5 vs SHA- 256) and rationale; how to mitigate collision risk and when to fall back to byte-by-byte verification; strategies for streaming and hashing very large files efficiently; what metadata (size, modification time) you would check before hashing; and how you would integrate this into a deduplication workflow across directories or machines.