On Fri, 2012-03-16 at 16:35 -0400, J. Bruce Fields wrote:
> On Fri, Mar 16, 2012 at 11:14:04AM -0700, Alexandre Depoutovitch wrote:
> > Hello,
> > I am trying to do random sector aligned writes to an NFS mounted disk. The
> > performance is order of magnitude worse than 4K (file system block size)
> > aligned I/O.
> > The reason is that NFS demon (Linux kernel 2.6.32) on the server side
> > always does buffered I/O, which behaves poorly for block unaligned
> > requests.
> > Is there a way to tell NFS daemon to use direct I/O?
>
> No.
>
> > If not, is it an implementation limitation or there is a fundamental
> > problem with using direct I/O in NFS server?
>
> I'm shamefully ignorant of Direct IO....
>
> If we supported Direct IO, are there heuristics that would let the
> server figure out on its own when it helped and when it didn't? Or
> would the administrator be stuck trying to figure that out?
>
> Is Direct IO possible from kernel buffers these days? Are there
> alignment restrictions?
Work is on its way to allow direct i/o from kernel buffers, but it is
not possible with existing kernels.
Have patience.
--
Trond Myklebust
Linux NFS client maintainer
NetApp
Trond.Myklebust@xxxxxxxxxx
www.netapp.com
��.n��������+%������w��{.n�����{��w��� jg��� �����ݢj����G���� ���j:+v���w�m������w�������h�����٥
