On Tue, Feb 18, 2025 at 4:05 PM, William Herrin <bill@herrin.us> wrote:

On Tue, Feb 18, 2025 at 12:16 PM Drew Weaver <drew.weaver@thenap.com> wrote:

I found out that this was an issue when I reloaded the switch and the filesystem looks like it rewound itself to 2022 in Aboot.

I've seen this before with MicroSD cards in a Raspberry Pi. The card stops accepting writes but continues to report write success to the OS.



My favorite was a "Sony 480GB Flash Drive" which I purchased at an electronics market in Beijing in 2010, for around $5 USD. I knew that it couldn't be real, but I figured it would be a entertaining…

It reported itself to the OS as having 480GB of capacity, but actually only had a 16Mb flash chip. Anything that you wrote past the and of the storage would wrap around to the start. 
It actually turned out to be remarkable useful - I mounted it on /var/log/syslog on a server, and magically had circular buffer of logs which would never fill up / run out of space….

W


On the Pi, this eventually shows up as seeming filesystem corruption when blocks are flushed and then reloaded to the disk cache. Upon reboot, the Pi reverts to the state it was in when the writes actually stopped happening.

I'm not really sure what the theory behind designing cards this way is. It does mean that the OS will boot even if the boot process must write to succeed, but it also means that the OS has no idea that the flash drive has failed and experiences odd random faults instead.

Regards,
Bill Herrin

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William Herrin