How to verify a copy is identical before you delete the original

A file that “looks fine” can still be damaged. A SHA-256 fingerprint changes completely if a single byte differs. RoomDisk compares fingerprints on both devices for every file.

What RoomDisk does

The sending device computes each file’s SHA-256.
The disk writes the file, reads it back and computes it again.
Only matching files are counted as safe to delete.
Each batch writes a receipt (text, JSON and a .sha256 checklist) on the disk.

Check it yourself

Mac / Linux: shasum -a 256 "photo.heic"
Windows: certutil -hashfile "photo.heic" SHA256
All at once from the disk folder: shasum -a 256 -c ".sparedisk/receipts/<receipt>.sha256"

On the phone, Backed up? checks any files against the disk by content, not by name.

Why “it opened fine” isn’t enough

Copies can go wrong without any warning: a cable or drive that drops out mid-write, a flash drive with failing memory, or an app that renames or skips files. A damaged photo may still open, with a grey band or missing half. Comparing fingerprints is the only quick way to know every byte matches.

Check the whole disk later

Drives and old phones can develop errors over time. In the disk’s Settings, Check the disk re-reads every file and compares it with the fingerprint saved when it arrived, so you find a problem while the original still exists.

Questions

What is a SHA-256 hash?

A 64-character fingerprint calculated from a file’s contents. Change one byte and the fingerprint changes completely, so matching fingerprints mean identical files.

Is MD5 good enough?

For spotting accidental damage, MD5 usually works, but SHA-256 is the modern standard and is also safe against deliberate tampering.

Does checking slow the transfer down?

Slightly. Fingerprints are calculated as the file streams, so most of the work overlaps with sending.

Try it with the two devices you have

Free to start. Nothing to install, no account.

Open RoomDisk