ZFS performance degradation over time

[Garrett Moore]

No, I haven't isolated the cause to only be uptime related. In my original
email I mentioned that "as suggested by someone in the thread, it's probably
not directly related to system uptime, but instead related to usage - the
more usage, the worse the performance."

I've been starting my system with different combinations of applications
running to see what access patterns cause the most slowdown. So far, I don't
have enough data to give anything concrete.

This weekend I'll try some tests such as the one you describe, and see what
happens. I have a strong suspicion that rTorrent is to blame, since I
haven't seen major slowdowns in the last few days with rTorrent not running.
rTorrent preallocates the space needed for the file download (and I'm
downloading large 4GB+ files using it), and then writes to them in an
unpredictable pattern, so maybe ZFS doesn't like being touched this way?



On Wed, Jan 6, 2010 at 2:21 PM, Ivan Voras <ivoras at freebsd.org> wrote:

> On 3.1.2010 17:42, Garrett Moore wrote:
>
> > I'm having problems with ZFS performance. When my system comes up,
> > read/write speeds are excellent (testing with dd if=/dev/zero
> > of=/tank/bigfile and dd if=/tank/bigfile of=/dev/null); I get at least
> > 100MB/s on both reads and writes, and I'm happy with that.
> >
> > The longer the system is up, the worse my performance gets. Currently my
> > system has been up for 4 days, and read/write performance is down to
> about
> > 10MB/s at best.
>
> Are you sure you have isolated the cause to be only the uptime of the
> machine? Is there no other change between the runs? E.g. did you stop
> all other services and applications on the machine before doing the test
> for the second time? Can you create a big file (2x memory size) when the
> machine boots, measure the time to read it, then read it again after a
> few days when you notice performance problems?
>
>
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