[CentOS] unfsd scalability issues

Boris Epstein

borepstein at gmail.com
Wed Jun 13 13:55:40 UTC 2012

On Sat, Jun 2, 2012 at 2:50 PM, John R. Dennison <jrd at gerdesas.com> wrote:

> On Sat, Jun 02, 2012 at 10:59:13AM -0400, Boris Epstein wrote:
> >
> > A process implemented in the userland may not be as efficient as one
> > implemented as part of the kernel - but that doesn't mean it can't scale
> > well, does it?
> Depends on ones definition of scale I suppose.  I consider efficiency
> and performance one factor of scaling.  To be completely honest about
> this I must admit that I've not spent a lot of time benchmarking any
> user space implementation in a large deployment but I wouldn't expect
> performance to ramp up based on scale.
> I've always had a strong aversion to file systems implemented in
> user space versus kernel space as I've (personally) never found such an
> implementation that had what I considered good performance.
> My needs, however, are not yours.  If your requirements give you leeway
> for higher latency and slower overall performance perhaps a userland
> file system will work perfectly fine for you.  As with all else in the
> IT sector use what works best for you :)
>                                                        John
> --
> Human beings hardly ever learn from the experience of others.  They learn;
> when they do, which isn't often, on their own, the hard way.
> -- Robert Heinlein (1907-1988), American science fiction writer, Time
>   Enough for Love (1973)

To be specific, I use UNFSD to export a MooseFS file system. MooseFS, by
the way, is userland-process based too.

Be that as it may, I've seen situations where a comparably configured
MooseFS client get to read at, say, 40 MB/s - which is fine - but the UNFSD
at the same time reads at 40K/s(!) Why would that be? I mean, some
degradation I can dig but 3 orders of magnitude? What is with this? Am I
doing something wrong?

I can't believe it works the same way for everybody - who would use it if
it did?


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