Verified card offload, in plain terms

What goes wrong, and why you do not see it

A drag-and-drop copy in the Finder reports success when the write calls return. It does not read anything back. If a byte was mangled in the reader, in the cable, in the drive's cache or on the medium, nothing in that workflow will notice — and you will find out months later, in the edit, on the one shot you cannot get again.

Comparing file counts and folder sizes does not help either. A truncated file has a size. A corrupted file has exactly the right size.

What Card Offloader does instead

1. Detects the card and scans it Every file, including the ones people forget: sidecars, hidden files, the manufacturer's folders. You can filter what gets copied, and you can point it at an ordinary folder instead of a card if the material already came off a drive.
2. Reads the card exactly once The bytes are hashed as they stream and written to every destination you selected, in parallel. Three destinations do not mean three reads of the card — the slow, wearing device is touched once.
3. Flushes every destination device Each drive is asked to commit its write cache to the actual medium before anything is checked, so verification reads the disk rather than a cache that agrees with itself.
4. Reads every file back and compares From each destination, with the operating system's cache bypassed. A mismatch is a hard, red, blocking failure — never a warning.
5. Writes the reports CSV and PDF in every tier. On Pro, an ASC MHL manifest that any MHL-aware tool can validate without our involvement, plus the camera report.

The folder tells you the truth even if the Mac dies

This is a small idea that does a lot of work. If the Mac crashes, if the power goes, if you close the lid and walk away, the state of the job is not held in an app that is no longer running — it is written on the folder, in words, where you will see it tomorrow morning or next month.

We tested the ugly version of this on purpose: card pulled physically out of the reader mid-copy, twice. 937 files across three destinations came out byte-identical to the source with zero partial files, checked with an outside tool. The test and its conditions.

What it will never do to your card

• Delete files from the source
• Move files instead of copying them
• Rename anything on the card
• Format or erase the card, even with a confirmation dialog

None of these exist in the application. Not disabled by default, not buried in preferences behind a warning — absent. The sandbox, the type system and an automated test all enforce it, because the one irreversible mistake is worth three layers of prevention.

Formatting a card is a job for the camera that will shoot it, and it should happen after you have looked at a report that says every file verified.

Where the copies can go

Read-back verification applies to remote destinations too. If verifying over the network is impractically slow for your setup, that becomes an explicit choice you make and it is recorded in the report — never something the software quietly downgrades to look fast.

Where we are not the answer

If one verified local copy is all you need, several free tools do that well, including some on the Mac App Store, and our own free tier does it too. Paying for Card Offloader makes sense when you need several destinations at once, a NAS in the loop, or a report you can hand to a client.