Don't Run Home Assistant Off a microSD Card
The most common way a Home Assistant setup dies is a worn-out memory card. Why it happens, how it fails, and the cheap fix.
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If you take one piece of hardware advice from this site, make it this one.
The single most common way a Home Assistant setup dies is a worn-out microSD card. Not a bad integration, not a botched update — the storage quietly wearing out and taking the configuration with it. It happens months in, long after you’ve stopped thinking about hardware and started depending on the thing.
Why cards fail here specifically
Home Assistant is unusually hard on storage, in a way that isn’t obvious.
It isn’t writing large files. It’s writing constantly and in tiny increments: every state change, every sensor reading, the logbook, and — the big one — the recorder database. A house with a couple of dozen entities generates a steady stream of small writes, all day, every day, forever.
Flash memory wears out per erase cycle, and microSD cards manage that wear with much simpler controllers than an SSD. They’re designed for cameras and phones, where you write a photo occasionally and read it back a lot. That is close to the opposite of this workload.
The result is a card that tests fine, benchmarks fine, and then doesn’t.
How it actually fails
Rarely a clean death. The failure mode is worse than that, because it’s ambiguous.
- The web UI gets sluggish, then times out occasionally
- An automation stops firing, with nothing useful in the log
- An integration won’t load after a restart
- The database throws corruption errors
- A restart takes far longer than it used to
- Eventually it won’t boot
The reason this is nastier than a hard failure is that every symptom looks like a software problem. People spend a weekend removing integrations and reinstalling add-ons, chasing a fault that was never in the software.
If your setup was fine and is now mysteriously flaky, suspect the card before you suspect your configuration.
What to do instead
Boot from an SSD. That’s the whole fix. A USB 3 SSD in an enclosure is inexpensive, dramatically more durable, and noticeably faster — restarts and history queries in particular.
The fix — the cheapest insurance you will buy for this project
- USB 3.0 SSD + Enclosure — Boot from this instead of the microSD. It's the single upgrade that most reduces the odds of losing your setup, and it's noticeably faster.
If you bought a Home Assistant Green, this is already handled — it has proper onboard storage and none of this applies. That’s a genuine and underrated argument in its favour.
Or sidestep it entirely
- Home Assistant Green — The shortest path to a working setup — plug in Ethernet and power and you're running tonight. Skip it if you actually want to learn what's underneath, or if you plan to run other services on the same box.
If you’re staying on a card for now
Sometimes that’s the practical answer — you’re trying it out, or the SSD hasn’t arrived. Reasonable. Reduce the damage:
Buy a good card. An A2-rated card from a real brand handles this workload far better than a bargain-bin one. Still not a permanent answer, but a real difference.
If you must use a card — fine to start on, and worth keeping as a spare
- 128GB microSD (A2) — Fine for getting started and for keeping a spare on the shelf. Not what you want as a permanent boot device — Home Assistant's constant small writes kill cards, usually with no warning.
Cut the write volume. In configuration.yaml, recorder accepts an exclude block. Excluding chatty entities you never look at historically — signal strength sensors, uptime counters, anything updating every few seconds — reduces writes substantially. Shortening purge_keep_days helps too.
Back up off the device. Non-negotiable on a card. Settings → System → Backups, scheduled, with a copy somewhere else. A backup stored only on the failing card is not a backup.
Keep a spare, flashed. Cards are cheap. Having one ready turns a dead-hub evening into a twenty-minute restore.
Isn’t this overblown?
Fair challenge, and there are people running on cards for years without incident. Cards vary enormously in quality, and a small setup with a trimmed recorder writes far less than a large one.
But the asymmetry is what settles it. The upside of staying on a card is a modest saving. The downside is losing your configuration at an unpredictable moment, usually with no warning, in a way that presents as a software fault and wastes a weekend before you find it.
That’s a bad trade for the money involved.
What to Read Next
- The Complete Home Assistant Starter Kit — everything else, in buying order
- Home Assistant Green vs Raspberry Pi — the hub that sidesteps this entirely
- The gear I actually run
Lost a card and have a war story? Post it in the comments — they’re the most useful thing on a page like this. Or email [email protected].