The 3-2-1 backup rule for video footage

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What "3-2-1" actually means

The 3-2-1 rule is the standard data-protection guideline used everywhere from IT departments to film sets. It's three short numbers:

• 3 copies of every clip: the original plus at least two backups. More copies means more independent chances that one survives.
• 2 different media: don't keep all copies on the same kind of device. Two copies on two identical drives from the same batch can fail the same way; a drive and a cloud account fail independently.
• 1 off-site: at least one copy lives somewhere else physically. If the location burns, floods, or gets robbed, the off-site copy is untouched.

For footage, a practical 3-2-1 setup is copy 1 on your primary shuttle/working drive, copy 2 on a second drive (kept separately), and copy 3 in the cloud or carried home in a different bag. The camera card is not counted as a long-term copy, since you're going to format it and shoot on it again.

How many backups of footage do you really need?

Two thresholds matter, and they're different:

Why one drive is not a backup

This is the mistake that loses footage most often: someone offloads the card to a single external SSD, formats the card on the spot, and calls it done. Now there is exactly one copy of an unrepeatable shoot, on a device that can fail without warning.

One drive is a single point of failure, and drives fail in ways you can't predict:

• Hardware death: controllers fail, SSDs brick, spinning disks click and stop.
• Physical damage: dropped on set, soaked in a coffee spill, crushed in a bag.
• Theft or loss: a bag walks off, and with it your only copy.
• Silent corruption: bad sectors and bit rot can quietly damage files that still "open fine" until the exact frame you needed is broken.

A backup means a second, independent copy that survives when the first one doesn't. Two copies on the same drive are not really two copies, and two copies that fail together are not 3-2-1. That's why the rule insists on different media and an off-site location, so the failure of any one thing can't take everything.

Verify every copy — "copied" doesn't mean "intact"

Making three copies is only half the job. The other half is proving each copy is actually good. A normal drag-and-drop copy in Finder reports success when the bytes have been written; it does not read them back to check they match the source. Cables glitch, drives have bad sectors, and a copy can finish "successfully" on a file that's silently truncated or corrupt. You won't find out until you're in the edit.

That's what checksum verification is for. The tool calculates a fingerprint (a hash) of every source file, copies it, then reads the destination back and recomputes the hash. If the two match, the file copied bit-for-bit; if they don't, you get an error instead of a silent loss. On film sets this is standardized as ASC-MHL (the American Society of Cinematographers' Media Hash List), the same verification approach used for professional delivery. A 3-2-1 plan made of unverified copies is just three chances to be holding three broken files.

How to apply 3-2-1 to footage, step by step

1. Copy 1 — primary drive, verified. Insert the card and copy every file to your main external drive. Verify with checksums so you know each file landed intact. Keep the card full for now.
2. Copy 2 — different media. Make a second copy on different media: a second drive, or a cloud account. Don't rely on two identical drives from the same batch. Verify this one too.
3. Copy 3 — off-site. Get one verified copy off-site: upload to Google Drive or Dropbox, or carry a drive home in a separate bag. This survives theft, fire and flood at the location.
4. Verify, then (and only then) wipe. Confirm every copy verified. Format and reuse the card only after two or three verified copies exist, never before.

Where Copsy fits

The 3-2-1 rule works with any tool. You can do it with any reliable copy-and-verify workflow. Copsy just makes the on-set part fast and hard to get wrong: plug in the card and it auto-detects it by content (Sony, ARRI, Blackmagic, RED, Canon, drones, audio recorders), then copies your footage to an external drive and, optionally, to Google Drive or Dropbox, in parallel, verifying every file with ASC-MHL checksums as it goes. It organizes by date and source and pings you on Telegram when it's done.

In one pass that gets you a verified local copy plus an off-site cloud copy across two media. Add a second drive for the full three copies and you've got real 3-2-1, and every copy is verified rather than just copied. Copsy is free today, no signup, no card limit, on macOS 13+.

See how the drive + cloud parallel copy works →

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