NFSv3, ZFS, 10GE performance

[Rick Macklem]

Bob Friesenhahn wrote:
> On Wed, 28 Mar 2012, Rick Macklem wrote:
> >>
> >> Hopefully, readahead doesn't kill performance for smaller files..
> >> :-)
> >>
> > Well, readaheads only happen if the file is large enough for the
> > readahead
> > to be before EOF. As such, they just won't happen for small files.
> 
> The real problem is for applications which do a seek and a new read
> prior to consuming all the data which is being read ahead on its
> behalf. This results in read amplification and increased latency for
> the next seek+read.
> 
Yes, random reads on a large file is a problem, as you noted before.
(I was just clarifying the "small file" case and it's good that you
 are clarifying the "large file, non-sequential" case.)

As jhb@ noted, disabling read-ahead may be a good idea for the POSIX
hint.

Thanks, rick

> Bob
> --
> Bob Friesenhahn
> bfriesen at simple.dallas.tx.us,
> http://www.simplesystems.org/users/bfriesen/
> GraphicsMagick Maintainer, http://www.GraphicsMagick.org/