Choosing an SD card or SSD for Rivian Gear Guard
Updated · by the Overlook team at CTT Apps (about us)
A Rivian is hard on storage. It records several cameras at once, keeps the drive full, and records over the oldest footage day after day. Storage that’s fine for photos can fail Rivian’s setup test, drop footage, or wear out within months. This guide explains what the labels on SD cards and drives actually promise, which ones matter for Gear Guard, and how to check what you bought.
What the car does to a drive
- Steady writing. Recording all four cameras takes roughly 4 to 6 MB/s, for as long as the car records.
- Small writes in between. Every file the car creates and extends also updates the filesystem’s tables, which are small writes in other places on the drive. That’s the random-write part.
- A speed test. When the car sets a drive up, it tests it and wants about 20 MB/s. Rivian’s owner’s guide asks for at least 20 MB/s of random writes.
- Endless overwriting. Once full, the drive is rewritten from end to end over and over. That’s what wears flash memory out.
On an Overlook Cache there’s one more load: while the car writes, the Cache reads the same storage to back recordings up. That’s why the Cache wants at least 10 MB/s of sequential writes, comfortably above what recording alone needs.
Reading the labels
| Label | What it guarantees | Useful here? |
|---|---|---|
| Class 10 (C10), U1 | 10 MB/s minimum sequential write | Barely: no margin, says nothing about small writes |
| U3 | 30 MB/s minimum sequential write | Good |
| V30 (also V60, V90) | 30 MB/s sustained sequential write, for video | Good: “sustained” is the point |
| A1 | 1,500 random reads and 500 random writes a second (4 KB), 10 MB/s sustained | The minimum for small writes |
| A2 | 4,000 random reads and 2,000 random writes a second (4 KB), 10 MB/s sustained | Better, if the device supports it (below) |
| “High endurance”, “Max endurance” | Rated for continuous recording, usually as hours of video or a warranty for dashcam use | The most important one for a car |
| “Up to 200 MB/s” | A best-case read speed | No: it tells you nothing about writing |
Why random writes are the hard part
Do the arithmetic and the labels look thinner than they sound. 20 MB/s of random writes at 4 KB a write is about 5,100 writes a second. An A2 card promises 2,000, which at 4 KB is only about 8 MB/s. At 16 KB a write, 20 MB/s is about 1,300 writes a second, which a good card can manage.
The labels are minimums under a standard test, and good cards do better, particularly with larger writes. But the label alone can’t tell you whether a card will pass. We don’t know what size of write the car’s own test uses, so the honest answer is to measure.
One more wrinkle with A2: its extra speed relies on the device using the card’s command queue and cache. Many card readers, cameras and older computers don’t, and run an A2 card at roughly A1 speed. Recent Raspberry Pi OS supports it on the Pi 5. An A2 card is never worse than A1, but don’t count on the difference everywhere.
Endurance: how long it will last
Flash memory survives a limited number of rewrites. Cards sold as “high endurance” or for dashcams are built and rated for continuous recording; ordinary cards are not, and in a car the difference can be months versus years.
A rough way to think about it: count how many times the whole card gets rewritten. A 256 GB card in a car that records two hours a day at 5 MB/s takes about 36 GB a day, one full rewrite a week. The Overlook Cache keeps exactly this count and flags a card as “showing wear” once about 600 times its size has been written, which is well inside what a high-endurance card is rated for and around where ordinary cards start failing.
Wear doesn’t announce itself. A failing card tends to show up as read or write errors in the system log, filesystems that need repairing after a power cut, and writes that get slower over weeks as the card runs out of spare blocks. The Cache watches all three and weighs them together into ok, showing wear or replace soon.
SD card, USB drive or SSD?
| Storage | Where | Strengths | Watch out for |
|---|---|---|---|
| High-endurance microSD (A2, V30) | Overlook Cache | Small, cheap, simple | Wears with use; small writes vary a lot by model |
| USB flash drive | Directly in the car | Plug and go | Many slow down badly once their fast cache fills, and run hot; check sustained writes |
| Portable USB SSD | Directly in the car, or a Pi 4/5 Cache | Fast, much more endurance | Bigger; draws more power |
| NVMe SSD on an M.2 HAT | Pi 5 Cache | Fastest, most endurance, reports its own health | Needs a Pi 5 and a HAT; see the build guide |
What we recommend
- Plain drive in the car: a portable SSD of 256 GB to 1 TB, or a USB flash drive whose reviews show sustained write speed well above 20 MB/s.
- Overlook Cache on its SD card: a 256 GB high-endurance A2 card, such as the Samsung PRO Endurance or SanDisk High Endurance lines. About three quarters of the card becomes the car’s drive, so a 128 GB card leaves only about 100 GB, under Rivian’s 128 GB minimum. Take 256 GB.
- Overlook Cache, best: a Pi 5 with an NVMe SSD, the SD card only holding the system.
- Pi Zero W: its card interface is slow, and the car’s setup test often fails on it. A Zero 2 W with an A2/V30 card, or a Pi 4 or 5, gets through reliably.
Test what you bought
Check it’s real
Counterfeit cards report a bigger capacity than they have and silently lose data once the real space runs out. Test a new card before trusting it with footage: H2testw on Windows, or F3 (f3write and f3read) on Mac and Linux, fill the card and read it back.
Measure its speed
The Overlook Cache measures the storage the car’s drive lives on a minute after it starts and then weekly: 64 MB written in 4 MB pieces and flushed to the card (sequential), then 16 KB and 4 KB writes at random places, flushed (random). It reports the results against what the car needs, and the in-car check flags a card below 10 MB/s sequential or under 500 random 16 KB writes a second. Weekly is deliberate: often enough to catch a card slowing down, rarely enough not to wear it.
For a plain drive on a computer, any disk benchmark that reports random 4K writes gives you a comparable number. Look at write results, not read.
Troubleshooting and questions
The car says “Speed testing could not be completed”
The drive (or the Cache’s card) didn’t reach the speed the car wants during setup. Try a faster drive. On a Cache, the “fast writes” setting (on by default) lets the car’s writes land in the Pi’s memory first, which helps a slower card pass, at the cost of losing the last few seconds of writes if power is cut right after a burst.
Is a bigger card more durable?
Yes, in a sense: with more space, each part of the card is rewritten less often, so the same driving wears a 512 GB card about half as fast as a 256 GB one of the same type.
My card is A2 but tests like A1
The device isn’t using A2’s command queue. That’s normal in many readers and older computers.
How do I know when to replace it?
On a Cache, when it says “replace soon”. On a plain drive, when recordings go missing, won’t play, or the car starts asking to format it.
Should I buy the biggest drive possible?
Rivian supports up to 2 TB. Beyond the extra days of footage it holds, bigger also wears more slowly. Speed and endurance matter more than size, though: a large slow drive is worse than a smaller fast one.
Related guides
- FAT32 or exFAT for your Rivian’s USB driveThe car records to both. What actually differs, the size and speed Rivian asks for, and how to format each.
- Building an Overlook Cache with a Raspberry Pi 5, with or without an NVMe SSDTwo complete builds with every part linked, assembly, setup, moving the car’s drive to the SSD, and troubleshooting.
- When your Rivian’s USB drive is full: overwriting and backing upHow much recording fits, what gets overwritten, and how to keep what matters.