Interesting Failure Modes – SD Card Arching

August 22nd, 2016

I’ve been using Raspberry Pi computers for several years. A few months ago the Raspberry Pi B I had hooked up to my TV and running OpenElec, stopped working. The Pi was locked up and then wouldn’t reboot when I pulled the power cord.

It’s an original B model, with just two USB ports, so I didn’t think much of it. I prepped and put in place a replacement Pi, also running OpenElec, and threw the Pi into a drawer for further inspection..later. I got 4 years faithful service from a $35 computer so I wasn’t complaining.

Some weeks later, I had an idea that I wanted to use a Raspberry Pi for so I grabbed the questionable unit and got to work.

My standard way to prep a Pi is to use raspbian-ua-netinst (https://github.com/debian-pi/raspbian-ua-netinst/). It doesn’t require a huge download, and it doesn’t automatically install a GUI and a bunch of software I don’t want.

I knew that this Pi, and this same SD card, were from the failed system so I started by running some tests on the SD card before attempting the install. I didn’t have any trouble with the SD card, so I proceeded. Much to my surprise, the Pi booted the new SD card and completed its installation without any issue.

Bit of a head scratcher but it was working.

Since then the Raspberry Pi has been handling duties as a simple Stratum 2 NTP server (More on that in a later post…). It’s not seeing heavy load but it’s been working fine.

This morning, while logged into the Pi and monitoring NTP, the system just stopped being able to see the SD card. Since I was already logged into the system via ssh, my session stayed active but I couldn’t run any programs and my simple ntp watching command (watch -n 1 ntpq -p), started to return a blank screen. I quit the watch app, tried to ‘ls’ and ‘cd’ but the system just said command not found. I wasn’t even able to shut down normally, since the shutdown app wasn’t available either.

I pulled the SD from the Pi and plugged it into another SD card reader on a different system. Everything looked Ok and I was able to run fsck without any errors. I plugged the SD card back into the Pi and it didn’t even try to boot.

I went through a couple other little tasks, extra fsck runs, etc., and then, while holding the SD card, I noticed that the interface side was slightly arched. When place on a flat surface, contacts down, the card was raised in the middle. Obviously, this minor elevation change had stopped all of the contacts from making a good connection to the Pi.

I inserted the SD card back into the Pi, and while holding the center of the card down flat against the contacts, I applied power and was greeted with a normally booting system.

Interesting.

I pulled the card out and flexed it, just a little, a few times until it sat more flat and the Pi is now working again normally.

The Raspberry Pi is working great but the SD card has started to lose it shape after 4 years of near constant use. I’ve been toying with the idea of using an old 1U server case to rack mount a couple of Raspberry Pis and then using the SD card just for booting, using an external USB disk to host the OS. That idea is starting to make even more sense to me now. That being said, I suspect the SD card arching issue would be less likely to occur on all of the newer Pi models, which use MicroSD cards instead. They aren’t made from multiple pieces of plastic clipped together, like most SD cards.

Just an interesting failure mode that I thought ought to be shared…

Topslakr

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