(File System) ReFS for Data Integrity

✅ Why ReFS is Better for Data Integrity

1. Checksums on Metadata and Optional Checksums on Data

• ReFS automatically checksums all metadata (e.g., file records, directory structures).
• You can optionally enable checksums on file data using integrity streams.
• These checksums are validated during reads. If there's a mismatch, ReFS knows the data is corrupt.

2. Built-in Data Scrubbing (Integrity Scanner)

• ReFS supports a background scrubber that scans volumes for corruption proactively.
• It compares checksums to actual data and detects bit rot, silent corruption, or disk-level issues.
• This is done online (without taking the volume offline), making it ideal for always-on workloads.

3. Integration with Storage Spaces / S2D: Auto Repair

• When combined with Storage Spaces or S2D, ReFS can automatically repair corruptions.
• If a corruption is found and a redundant (mirrored/parity) copy exists, ReFS:
  1. Reads the correct copy from another physical disk.
  2. Automatically replaces the bad block on the corrupted copy.
• This process is transparent and online — no downtime, no manual intervention.

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🔧 How ReFS Fixes Corruption Online (Example)

Let’s say you have a 3-way mirrored volume on S2D using ReFS.

• One disk has a bit-flip or sector corruption in a data block.
• ReFS, during a read operation or scheduled scrub, checks the checksum.
• The checksum doesn’t match — corruption is detected.
• ReFS uses S2D to read from one of the other two healthy copies.
• It writes back the corrected block to the corrupted disk — automatically fixing it.

This whole process happens while the system is online, and without data loss.