#403 Simple Trick to protect your Raspberry SD card from Crashing

SD cards in Raspberry Pi computers wear out and die after a while because they are not made for computer usage, and many write cycles. In addition, the SD cards can become corrupted if the Pi loses power without a proper shutdown. We have several possibilities to avoid this disaster. Only one is simple and cheap. But, unfortunately, it has its caveats. So let’s get an overview and use a nearly unknown Raspbian feature to help us solve the problem.

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[magoostus]

there is another option using write-behind caching on EXT4 so it caches all the writes to ram and then using the COMMIT=xx seconds mount option it will write the changes from ram to disk every so often, the best of both worlds

[dirkj]

SD cards are not by definition unreliable. They come in different flavors for different use cases. If you pick the right one, an SD card can be more reliable than a big cheap SSD.

The most important criteria are the cell technology used and the Bill of materials.




Cell technology:
* Most consumer cards use TLC or QLC (3D) cell technology. A single cell can typically be rewritten approx 200 to 300 times.
* Some consumer cards advertise with 'long endurance' or 'industrial' terms. Often such cards use MLC cell technology (but this is not guaranteed!). In this case a single cell van typically be rewritten approx 2000 to 3000 times. This type is also often used for EMMC memory and modules.
* For more demanding environments (automotive, medical, extreme conditions, ..), often (p)SLC cards are used. For these type of cards, a single cell can be typically rewritten up to 30000 times. That's >100 times more than a typical consumer card!. You will not find these cards in a regular (online) shop. Cards utilizing this technology often have more advanced flash controllers onboard providing additional security and features compared to consumer grade cards (e.g. power failure protection, better wear leveling...).



Bill Of Materials:
* Most consumer cards do not have a fixed Bill Of Materials (BOM). This means the internal components can change without notification and the manufacturer will choose whatever is available and the cheapest that complies more or less with the specifications. So for one batch of cards, the cells can be TLC, and a few months later, QLC becomes cheaper and the manufacturer switches to QLC components, or uses another flash controller... This is also the reason why almost no manufacturer will give the complete specifications of the used components for these cards.
* Most manufacturers also offer fixed BOM cards. These are cards where the used components are fixed and will not change without notice. This guaranties that if you buy the same card next year, it will behave exactly the same as the ones you already have.



An example of a 'cheap' (p)SLC card with fixed BOM is the SDSDQED-016G-XI model by Western Digial/Sandisk.
It is a 16GB SLC card with an extended temperature range (-40+85C) and an endurance of 480TBW. It costs about 30 euro's at Mouser. This is typically cheaper than a usb->sata/M2 adapter + decent SSD.

For comparison: a Kingston A2000 SSD of 500GB has an endurance of 360TBW. And if you only look at smaller very low cost ssd's, then the endurance is often <100TBW ((e.g. Kingston A400 120GB -> 40 TBW)




So for projects that do not depend on very high speed disk access or require a lot of storage, such SD card is unrivaled. Both for price and reliability.


(The explanation above is a bit simplified... there are other factors playing also a role, but this comment is already long enough for now :-)

[kingggerald]

This came just as I needed it!
Releasing 24 dashboards driven by raspberry pi's next week and was worried about configs being changed and other (python) code config that needs to write to the memory! Much appreciated Andreas!

[peter.stimpel]

I was able to reduce my sd card consumption drastically by logging to my remote homeserver. (almost) No local logs anymore. There is another advantage in remote logs: you can find suspects, even after the device in question died. Since there is a homeserver up and running 24/7, it was just a matter of some simple configuration.

[abcmeins]

YES! Finally I can cut the power to my rasppi whenever I want without the fear of destroying the SD-Card!

[NikolayH]

It is also very useful to mount the filesystems with noatime, nodiratime options in order to avoid updating access time in the file and directory attributes each time the file or directory is accessed, no matter it was just read.

[EsotericArctos]

With the newer Raspberry Pi 4 with the higher RAM this overlay makes a lot more sense now. I guess you could use read/write Boot drive and periodically copy the overlay to the SD or to an external network drive for data that may need to be kept longer term. Thanks for the great information.

[bern]

Thanks Andreas, I was worrying about my sd card in. my headless Raspberry Pi 4 recoding NOAA weather images 24/7 so I made images of the card if it fails, I haven't had any card fail yet but you saved the day and me worrying, thanks for this tip will implement it : )

[GiacomoCatenazzi]

I use a different approach, and I find it much simpler and scalable: I use a NAS, so shared directories to save logs and data. So I get automatically backups (I need to set up only once for the base directory in the NAS), fast disk (but it depends also on network), cheap disks. And I'm able to split or merge services and rpi much easier.

[misteragony]

I also tend to install ZRAM on every pi I own. It removes the need for swap space on the sdcard and it allows you to fit about 50% more stuff into the physical available RAM.

[McTroyd]

IIRC, OpenWRT uses OverlayFS, but their implementation is pretty static without lots of hackery. Really neat the Pi Foundation was able to simplify it down to a toggle switch! 👍

[gunter]

Very useful video, Andreas👍- this setup is indeed ideal for 24/7 applications that do "something" and send the results to a remote server or such. Or another idea: Run Minikube on the Pi4 and push containers to it from remote. That way the Pi would become application-agnostic?

[NotMarkKnopfler]

I use RAMFS and mount it over the top of the log directories. Then, when a program writes to the log files in the log directory they are intercepted by RAMFS instead. When the max size is reached they are discarded. They are never written to the SD card. My SD card is in its 4th year of operation (as a LoRa gateway) with no problems so far.

[WoLpH]

In addition to these tips I would strongly recommend getting an SD card that's more suitable for this kind of usage. I've personally had good results with the WD purple SD cards, I've got 3 pi's that have been running 24/7 for about 3 years now on an unmodified raspbian installation with full logging enabled (and one of them is constantly writing due to a pihole installation). So far I haven't had any issues. But... I would recommend partitioning only a small part of the SD card (i.e. 25% or so) so the wear leveling algorithms can do their thing and make sure your SD card won't run out of working blocks.

[gkseifert]

Thank you! Extremely useful, extremely inexpensive, reversable and can be done in seconds. Love it! The overlay wins for me.

[jdsan]

Thanks Andreas for the tip. What I do is to use a high endurance SD card, specially designed for high number of writing cycles ( they are used in security cameras). Is a very lazy solution though.

[bbogdanmircea]

After 2 SD cards busted, I put an SSD for my Home Assistant RPi4 and it is running since then very reliable, hope I don't jinx it. But very good tip to make the SD card last longer.

[anocco]

I saw this option before in dietPI, I think it's a cool feature, glad the ported it on raspbian too

[joels]

Add commit=300 as a mount option in /etc/fstab. EXT4 default is to commit all writes every 5 seconds. If you mount with commit=300 it will cache writes in memory then write them to disk once every 5 minutes. You can reduce your SD wear by 60x by adding that line.

[wktodd]

So, why isn't there an option to write the ram files back to sd on close? Thus dramatically reducing the writes