Avoid eMMC corruption without UPS

Merinorus · Post by **Merinorus** » 27 Aug 2019, 14:27

Hi everyone,

When we are using industrial PLC, whenever we plug it off, it will include a mechanism (capacitor, embedded software) to shutdown without corrupting the memory. So when the device is powered on later, we are ensured it will run again. Of course, we

I would like to expect exactly the same from the RevPi Connect+. Let say I have a program running with eMMC write (ie : logging) and the RevPi is plugged off during memory write : how to be sure the memory is not corrupt as an industrial PLC? Is there a hardware (embedded capacitor, wawtchdog...) or software way (filesystem) to act the same as an industrial PLC?

Same question with the hardware watchdog : if it acts as a hard reboot for the RevPi (the SoC powersupply is shut off during 1 second), how to avoid memory corruption?

Many thanks!
--
Antoine

Merinorus · Post by **Merinorus** » 16 Sep 2019, 17:08

Anyone ?

Post by **dirk** » 19 Sep 2019, 10:57

Hi Antoine, well sure a UPS is able to provide a safe way to reboot the device properly. I just can say hat we deal here with may devices every day. We are swiching them on and off without proper shutdown commands at all...
All I can say is that the Ext4 file system works pretty well here as this is a journaling file system.

elconfa · Post by **elconfa** » 12 Feb 2020, 11:16

So you can confirm that proper shutdown is not necessary? I'm looking to use the RevPi Core 3 for connecting to a web site inside my company. I will connect a 7 inch touch screen through micro HDMI and usb port for touch.
Do you think there is no problem shutting down taking out the power?
Thanks a lot
Massimo

Post by **dirk** » 14 Feb 2020, 12:00

Well I cannot guarantee that your systems will never be in such situations where data will be unpredictable losst. There is also a limited eMMC life time depending on the wear leveling etc. So just give it a try.

matthias.hefti · Post by **matthias.hefti** » 27 Oct 2023, 12:08

I'm also thinking about the power-fail safety of the RevolutionPI. How are the experiences from the field applications (customers)? Do you know about problems after power off?
Is there a hardware (capacitor or similar) to finish critical writing processes to the eMMC in case of sudden power off?

I'm thinking about using the RevPi Connect 4 as an IoT Hub inside industrial production machines. Sudden power off could happen daily. Can you recommend me the RevolutionPi for this use case without an UPS?

Post by **dirk** » 06 Nov 2023, 07:40

Hello Matthias, take a look at this FAQ entry: Revolution Pi Hardware FAQ | "Is there a recommendation for a small UPS in DIN rail format?"
We have designed the RevPi Connect for use together with an uninterruptible power supply. See also this article:
How to Connect UPS
The article shows a RevPi Connect 3+ - we are currently working hard to update the documentation - so here is the picture of the front of the RevPi Connect 4
https://revolutionpi.com/tutorials/revp ... -connect-4
From my experience, I can say that I have never had problems with a corrupt file system, even if I simply unplugged the device several times and did not shut it down correctly using the "shutdown" command.
There is quite a lot of discussion material in this direction in the forum if you search for UPS or USV, i.e. here (you have to translate them maybe)

In general, the ext4 file system which is used, i.e. in the current "Bullseye" image is a journaling file system that is robust and simply writes back journal entries that have not yet been synchronized after startup as if nothing had happened. However, there can always be a residual risk that justifies the use of a UPS.

Avoid eMMC corruption without UPS

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