[Arm-netbook] Logging and journaling

[Stefan Monnier]

> I just want to make sure of something: are the EOMA68-A20 computer cards
> going to be shipped with logging and journaling disabled (so that the
> storage isn't constantly being written to)? I'm asking because this is

FWIW, I think that journaling is a non-issue.  The underlying assumption
is that journaling causes more writes and hence ages the NAND faster.
While this is true in some cases, it's not true in all cases (the
reverse can also be true in some cases), and whether it's true in the
common case is still up for debate AFAIK.  Furthermore, even if when
it's true, the factor by which it is increased is small (IIRC the worst
case is a factor 2).

Now it's true that all those extra writes go to the same place on the
filesystem, so if your NAND's wear leveling sucks rocks, you'll kill
your NAND very quickly.  But if your NAND's wear-leveling is anywhere
close to honest, then journalling shouldn't make any noticeable
difference to the expected lifetime of your NAND.

There's been a few reports of people seeing that SD die after a fairly
short use of a journaling filesystem on it.  I don't think I've ever
seen conclusive evidence that the two were related (e.g. I've also seen
SD cards die even though they've never touched a journalling
filesystem), and I've seen lots of SD cards live long happy lifes with
a journalling filesystem on them.

So, IMO, go ahead and take advantage of the latest journalling
filesystem.  If you SD card dies, it's just that you got a lemon.

W.r.t to logging, I've agree that you're probably better off logging to
RAM (or to a remote host) than to a local "disk", and AFAIK that's the
default behavior of systemd anyway.


        Stefan