sd cards in raspberry pi computers wear
out and die after a while because they
are not made for computer usage and many
ride cycles
in addition the sd cards can become
corrupted if the pi loses power without
the proper shutdown
we have several possibilities to avoid
this disaster only one is simple and
cheap but unfortunately it has its
caveats
so let's get an overview and use a
nearly unknown raspbian feature to help
us solve the problem
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most it experts will tell you to create
regular backups of your computer storage
devices
that is necessary but not sufficient for
an engineer like me
i want to build a reliable system that
never needs to restore the backup
reliability with sd cards can be
achieved by avoiding extensive writing
however because this needs quite some
linux knowledge it is nothing for a noob
like me
so i had to find another way and
replaced the sd card with a more
reliable storage product the ssd
they are made for reading and writing
are much faster than sd cards have a
vast capacity and should run for years
with a raspberry pi
fortunately standard raspbian supports
usb boot out of the box and the
raspberry pi 4 has two fast usb 3
connectors
but unfortunately ssds have a few
disadvantages
the first is that they are mounted
outside the standard cases
i know you get specialized cases with
built-in ssd or m2 capability but they
are expensive
external ssds often are less expensive
but not as convenient
also because of the cable
the next disadvantage is that they cost
money and the third is that they block
one of the valuable usb 3 connectors
so ssds are a perfect fit for my home
automation server and i love this
possibility
but i have other lower end applications
of a raspberry pi for example the ttn
gateway on the roof the receiver for
weather balloons or the dmr hotspot for
amateur radio
all those applications should be compact
and cheap
they do not need to be extremely fast
and most of them do not need long time
storage of data
once they are configured they do not
change for a long time but i would like
that they lock important events for
analysis
photo frames and many other projects
have the same needs by the way
using an sd card would be perfect for
such use cases
but how can we make them reliable
as said before we have to drastically
reduce ride cycles on the sd card or
avoid them entirely during operation
older sd cards had a lock switch to make
them read only
the smaller microsd cards do no more
have such a switch and it anyway would
not work with standard raspbian because
it would refuse to work
fortunately we have a solution for that
case
bright people went through the whole
operating system to find out where it
writes to the sd card and in which
directories
because of the flexibility of linux they
created a list of commands to either
stop this writing or in the case of
important logging for example create a
memory disk and redirect their writing
like that they were able to create
viable solutions like this right up on
adafruit's site
unfortunately it is a lot of work to
copy paste all these steps into the
terminal
and in the case of the adafruit way it
does not work with a desktop version of
raspbian
fortunately the raspberry foundation
elegantly solved the problem
it creates a so-called overlay file
system in ram and redirects the right
traffic
like that the sd card can be read only
and raspbian still works in addition it
is much easier to use and it also works
for the desktop version of raspbian
let's try it out
we open raspberry pi configuration on
the desktop go to performance and to
overlay file system
there we hit enable and get two choices
we can create the overlay file system in
memory set the boot partition as read
only or both together
it warns us that we have to reboot to
get it working
we select both
after that we reboot and test
we create a file in our home directory
and add some text
everything works as usual if we close
the file and reopen it the text still is
there only if we reboot the file is gone
because it only resided in run
so the feature seems to work
it easily can be switched off again for
example if you want to upgrade your
system once in a while
this behavior is perfect also for
education where we often have several
raspberries and very creative users if
you know what i mean
with a read-only sd card we can let them
do whatever they want
if they overdid it or after the lesson
we just switch the raspberries off
next time we switch them on we are sure
the new user starts with a proper
configuration
maybe you use this feature also if you
want to test something and be sure that
you can revert to the old status here
you have to pay attention to three
things
because the overlay file system resides
in memory we have to have ram
i suggest using at least a two gigabyte
raspberry pi not all operations are
possible in this state the upgrade of
the eeprom was refused for example
all operations requiring a restart
cannot be performed because we would
lose all our installation work before we
are finished as the famous sisyphus who
cheated and was punished to pushing an
immense stone up a hill only for it to
roll down every time it neared the top
if we decide to use the light version we
can also use the terminal window to
select the feature
just type sudo raspy config and you find
it under performance as before
with this knowledge you can install your
lorawan gateway or any other simple
project and customize it to your liking
after that you hit the two switches and
your sd card will survive much longer
and you can still check the locks if
needed just do it before the next reboot
summarized we can avoid extensive
writing by
disabling unneeded logging
redirecting writing to ram disks with a
barefoot method like the one documented
by adafruit or use the standard raspbian
function to create an overlay file
system in ram
and set the sd card to read only
if this is not possible we have to
replace the sd cards with ssd drives
that was all for today as always you
find the relevant links in the
description i hope this video was useful
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