Hi.
>
> The real question now is: How long can a raspi run without crashing ?
>
As all *ni systems, a RasPI can run for years unless there is a hardware
failure or overheating. I've been (silently ;) ) collecting uptimes at work
and I've seen servers that haven't rebooted for 1600+ days
(enterprise-grade computers have redundand power supplies and hard disks
that can be hot-swapped/replaced). A RPi can perform the same.
>
> Eventually I will start logging usage of each segment, on each tube, and
> use that for depoisoning. Since it's a micro SD (flash) filesystem, which
> has limited write-cycles, I have to be careful about how often I store
> runtime information. Syncing daily to the same file (appending) could cause
> wearout after several years if the OS doesn't incorporate some form of
> levelling. Doing it every 3-4 days should get me about 100 years of logging
> if the flash has 10K write-cycle endurance. Not that I will be around then
> to do anything with that
>
Well, the write-cycle count applies to each single bit of the flash memory.
So, if you're just appending data to a file, what has been written won't
change on subsequent additions. Your filesystem might have blocks of 2 kiB,
4 kiB or 8 kiB, so that's the amount of data that could change at once if
the bucket was full yet. Then there's the filesystem internals and journal
("which blocks form a file" in simple terms, the index), that could change
more often.
OTOH Linux systems log stuff all the time to disk, so that part of the
flash disk might fail before your clock log sectors.
An option could be to upload your data to some online (free) service, since
you have WiFi.
Also, have you though of implementing a purely hardware watchdog to shut
down everything in case the software hangs?
Paolo
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