Re: Arista filesystem rewinding back 3 years

[Warren Kumari <warren () kumari net>]

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
>
> --
> William Herrin
> bill () herrin us
> https://bill.herrin.us/