SD cards for 4K video, SSDs and backups for a documentary shoot

The smallest object in a documentary kit is the memory card, and by the end of a shoot day it holds the most valuable thing you own: footage you cannot shoot again. A contributor will not relive a first day at a new job because a card failed. This guide covers how to choose an SD card for 4K video, which external SSD makes sense for offloading and editing, and the routine that puts two verified copies of everything on separate drives before a card is ever wiped.

Storage is the budget line people trim first, and in my view it is the worst place to save. Drives cost far less than a reshoot, and a lot of what follows costs nothing at all, because it is habit.

How much storage a documentary shoot needs

Start with the bitrate, not the card. Bitrate is how much data the camera writes every second, given in megabits per second (Mb/s). Multiply it by recording time, divide by eight to turn bits into bytes, and you have a file size. The video file size calculator in our Kit Room does the arithmetic, and its default example is a fair model for a modest documentary:

Two hours of recording a day is a reasonable planning figure for a mix of interviews and observation. A day following someone from breakfast to bedtime can run well past it, and observational films pile up hours quickly (our piece on editing a documentary from 200 hours of footage shows where they end up). Plan from your own shooting style, not mine.

Resolution and codec move these numbers fast. Apple's target for ProRes 422 HQ at UHD 3840 x 2160, 24p, is 707 Mb/s, about 318 GB an hour, four times the HD figure. Many mirrorless cameras record 4K in long-GOP codecs at far lower rates; at 100 Mb/s an hour is 45 GB, and at 200 Mb/s it is 90 GB. Put your own camera's setting into the calculator before you buy anything.

Choosing an SD card for 4K video

The number that matters for recording is the video speed class, printed on the card as V30, V60 or V90. It is the minimum sustained write speed the SD Association sets for that class: 30, 60 or 90 megabytes per second. Sustained is the point. Video is a long, steady stream, and a card that writes fast in bursts but stumbles over a minute will drop frames or stop recording. The large "up to" figure on the front of most cards is usually the read speed, which helps when you offload and does nothing for recording.

Camera bitrates are in megabits, card speeds in megabytes, so divide the bitrate by eight:

• 100 Mb/s is 12.5 MB/s. A V30 card has plenty in hand.
• 200 Mb/s is 25 MB/s. Still inside V30, with less margin.
• 400 Mb/s is 50 MB/s. That is V60 territory.
• Higher intraframe 4K modes push into V90.

The camera manual lists which card each recording mode needs, and the manual wins over my arithmetic every time. UHS-II cards have a second row of contacts and run faster in cameras and readers built for them; in a UHS-I slot they fall back to UHS-I speed.

Two more habits. Spread a shoot across several smaller cards rather than one huge one, because a single failure then takes less with it; I would rather lose 128 GB than 512. And buy from sellers you trust, since counterfeit cards with faked capacity do turn up. Format every new card in the camera and record a test clip before it goes anywhere near a contributor.

How the cards and drives below were chosen: from their published specifications and the makers' own documentation, favouring models with years of use behind them. They have not been tested by us. The SanDisk Extreme PRO 128 GB is a UHS-I V30 card, the common baseline for 4K on mirrorless cameras at long-GOP rates. The UGREEN reader is UHS-II, takes SD and microSD, and connects over USB-C, so offloads are not held back by a slow built-in slot. It reads a UHS-I card at UHS-I speed and is ready if your next camera takes UHS-II cards.

External SSDs for offloading and editing

An external SSD for video editing has no moving parts, which makes it faster than a spinning hard drive and more forgiving of the knocks a location bag takes. For a documentary shoot it does two jobs: it receives the first copy of every card, and it is the drive you edit from on the road.

The connector tells you little. USB-C is a plug shape, and the speed behind it depends on the USB standard both the drive and the computer support. The Samsung T7 Portable SSD 2 TB uses USB 3.2 Gen 2, a 10 gigabit per second interface, which is ample for ProRes HD and for most long-GOP 4K. The SanDisk Extreme Portable SSD 2 TB connects over USB-C and is built to resist water and dust, a sensible trait in the drive that lives in the field bag.

A portable SSD for video editing works best plugged straight into the computer with the cable that came with it, not through an unpowered hub or a long cable from a drawer. If you see slowdowns during very long copies, let the drive cool; small enclosures warm up. And use drives from two different makers for your two copies, so a fault in one product line cannot reach both.

At 2 TB each, either drive holds the 792 GB from the example with room for proxies and project files. If your shoot runs longer or in UHD ProRes, size up or bring more drives.

Offloading with checksum verification

Copying is not verifying. Dragging a card's folder to a drive moves the files, but nothing confirms that every byte arrived intact. A checksum is a short fingerprint calculated from the data, using a method such as MD5 or xxHash. Offload software calculates it on the card and again on each copy, and if the fingerprints match, the copy is good. Several dedicated offload apps do this, and DaVinci Resolve has a clone tool that verifies copies with checksums.

The routine, card by card:

1. Slide the card's lock tab to read-only before it goes in the reader, so nothing can write to it.
2. Copy the whole card with its folder structure intact, not only the clip files. Cameras keep metadata in folders and sidecar files that editing software expects to find.
3. Copy to both drives in one pass, with verification switched on.
4. Read the report. Any mismatch means copy that card again.
5. Open a few clips from each copy and scrub the start, middle and end.
6. Log the card number, date, camera, both destinations, the result and your initials.
7. Only then mark the card as ready to format.

Offload at lunch on long days and always before bed. A card that sits full overnight in a jacket pocket is a single point of failure with legs.

The 3-2-1 idea on a shoot

The rule archivists and IT people repeat is three copies, on two kinds of media, with one off site. On location it works like this. Until a card is formatted, the card itself counts as a copy, so in the field you have the card plus two SSDs. Once the card is wiped and back in the camera, the third copy has to exist somewhere else, and that is the job of a hard drive.

A portable hard drive gives you a second kind of media at large capacity. The WD My Passport 5 TB is a portable hard drive with space for several shoots of the size above. Spinning drives are slower than SSDs and less tolerant of being dropped while running, so treat it as the archive copy rather than the one you edit from.

Off site means not in the same bag, the same car or the same hotel room as the other two copies. Hand it to a different crew member, or send it home with whoever leaves first. Cloud storage can be the off-site copy once you are home, but do the sum first: 792 GB on a connection that uploads at 50 Mb/s takes about 35 hours.

Back at the office, a network drive (NAS) that the whole edit team can reach is a tidy home for the second copy of every project; UGREEN's NAS range is one option. It sits in the same building as the edit, so it does not replace the off-site drive.

Labelling, and the card you must not format

One rule matters more than the rest of this article: never format a card until two verified copies exist on two separate drives. Format in the camera, not on a computer, because the camera sets up the file system and folders it expects.

Labelling is how you keep that rule at the end of a fourteen-hour day. Number every card on its body, away from the contacts (A01, A02 for camera A), and use a card wallet with a fixed habit: empty cards face up, full cards face down. Name folders on the drives the same way every time, for example Day03, then CamA, then Card07, so a card number on the log points to one folder only. Label every drive with the project, its copy number (1 of 3) and a phone number in case it goes missing.

Write the last line of the day's call sheet before the first: who carries the cards at wrap, who offloads, and where each drive sleeps. Our shot list and call sheet templates have a line for exactly that.

Drives fail, so plan for it

Every drive fails eventually; the only question is when you find out. On location the usual causes are a drop, a cable pulled mid-copy, a drive unplugged without ejecting, a hot car, a spilled coffee, and cards that are counterfeit or simply worn out. SSDs can fail without warning. Hard drives sometimes give you a clicking noise first, and sometimes not.

So retire anything that has been dropped while running or has thrown an error, even if it seems fine afterwards. If a card reports an error in camera, stop recording on it at once and set it aside. Recovery software can sometimes rescue files from a card nobody has written over, and every new clip lowers those odds. After the edit, move the project and originals to fresh archive drives instead of trusting the shoot drives for years. They have had a hard life.

Questions

What SD card do I need for 4K video?

Check the camera manual for the recording mode you plan to use; it names the speed class required. As a rule of thumb, divide the bitrate in Mb/s by eight and choose a V class above that figure with margin: V30 covers most long-GOP 4K modes at 100 or 200 Mb/s, while higher intraframe modes need V60 or V90.

Is a portable SSD fast enough for video editing?

For most documentary work, yes. A portable SSD on a 10 gigabit per second USB connection handles ProRes HD and most long-GOP 4K comfortably. Plug it straight into the computer, use a good short cable, and keep a second copy on another drive.

How many copies of my footage should I keep on a shoot?

Three: the working SSD, a second SSD, and a hard drive kept somewhere else. That is the 3-2-1 idea of three copies on two kinds of media with one off site. Until a card is formatted it counts as one of the three.

Should I format SD cards in the camera or on a computer?

In the camera, and only after two verified copies exist. The camera builds the file system and folder structure it expects, which avoids recording errors on the day.