Trying to benefit from the atactl program and disk sleep mode on my
laptop, I mounted / with "nodevmtime" and "noatime" and /usr and /var
with "noatime".  I then set the disk standby-timer to 5 seconds and
the disk stops after 5 seconds of inactivity, just as expected.

However, the disk starts again every 30 seconds - thanks to update.

Why? :-)

Sure, cron writes to /var/cron/log every 10 minutes by default (and
cron has no options at all, so this can't even be disabled).  But
every 30 seconds?  AFAIK, "noatime" prevents filesystem modification
when a file (like crontab) is read, so there should be no need to
spin up the disk.  What's going on?

I have read on the mailing list that using "async" may help with this
problem - but that sounds like a dangerous solution to me.  I'd rather
use the default sync mount and have update (or sync(2)) touch the disk
only when something on the disk has actually changed and a sync is
really needed.  When the machine is idling (and something done to cron
to make it shut up :-), the disk could sleep all the time.

Maybe I'm missing something here?

  -jm