I've noticed that for sending big mails (10MB) it can take up to 30
min
until they are sent. So I investigated a bit into the problem. I
deactivated amavis and dkim, so they do not seem to be part of the
problem.
What happens is, that as soon as I write a bigger e-mail, the system
load goes up from 0 to around 2.5 and when the mail is send, goes back
to 0 again, but there is almost no cpu usage at all. So it should have
something to do with the I/O system I guess.
iotop tells me that cleanup is writing at around incredible 60 kb/s to
the disk.
All other processes work perfectly and don't get slowed down while the
mail is send, I can even copy to the same partition at normal speed.
It
is just cleanup which seems to be so slow. There is also still enough
memory left. Besides the speed, email delivery works perfectly, there
are also no log messages indicating anything.
I don't think it has to do with the network card since I also tried
out
smtp-source -t crap@localhost -l 102400000 127.0.0.1
Completes in a 1-3 seconds on a laptop (ssd) and old workstation
(rust). Obviously the problem is outside of Postfix.
Maybe the outpout from 'lsattr /var/spool/postfix' will reveal
special configuration (sync writes, or something else).
Decades of using Linux and I had no idea you could set sync writes on
file/directory level!
That was exactly the problem. Would be interesting to know how that ever
got set.
Thanks a lot. I really couldn't imagine in any way what the problem
could be...
