Re: Increase FreeBSD NFSv4 nfsd buffer size? Re: Increase default NFSv4 server size "max_block_size" to 4MB

On Tue, May 12, 2026 at 6:18 AM Cedric Blancher
<[email protected]> wrote:
>
> On Tue, 17 Mar 2026 at 00:35, Rick Macklem <[email protected]> wrote:
> >
> > On Mon, Mar 16, 2026 at 5:41 AM Chuck Lever <[email protected]> wrote:
> > >
> > >
> > > On Mon, Mar 16, 2026, at 3:51 AM, Cedric Blancher wrote:
> > > > As debated a while ago, can the default NFSv4 server size for
> > > > "max_block_size" be increased to 4MB, please?
> > >
> > > There is an administrative setting to raise this limit for
> > > recent versions of the kernel. Can you report your experience
> > > when you raise the limit? Hiccups, performance issues, etc? I
> > > would kind of like this exercise to be data-driven.
> > >
> > > What is still unknown to me is which NFS client implementations
> > > can support 4MB or 8MB. Without client support, an increase in
> > > the default in NFSD doesn't mean anything. Rick, Anna, Roland?
> > Although it has not seen much testing, it is possible to do a > 1Mbyte NFSv4
> > mount in FreeBSD.
> > For a 2Mbyte mount, (the only size > 1Mbyte I've tried) the settings would be..
> > In /boot/loader.conf
> > kern.maxphys=2097152
> > vfs.maxbcachebuf=2097152
> >
> > and in /etc/sysctl.conf
> > kern.ipc.maxsockbuf=9455616
> >
> > Then a mount will use 2Mbytes if the server supports it.
>
> How can I verify that the FreeBSD NFSv4 nfsd now uses 2M for NFS buffers?
The default is 128K. (You can see what it is via "sysctl vfs.nfsd.srvmaxio".)

With "main", you can increase that up to 4M by putting
nfs_server_maxio=N (where N can be up to 4194304 for "main" and 1048576 for 15)
- adding an entry in /etc/sysctl.conf for a larger value for kern.ipc.maxsockbuf
  (It will tell you the recommended minimum setting if you boot after
   putting nfs_server_maxio=N in /etc/rc.conf.)

rick

>
> Ced
> --
> Cedric Blancher <[email protected]>
> [https://plus.google.com/u/0/+CedricBlancher/]
> Institute Pasteur