Linux NFS client and FreeBSD server strangeness

Guido Falsi mad at
Wed Apr 4 19:14:26 UTC 2018

On 04/04/18 20:27, Mike Tancsa wrote:
> Not sure where the tweaking needs to happen, but I am getting strange
> behaviour between a Linux nfs client and FreeBSD RELENG_11 NFS server.
> The FreeBSD server starts with
> nfs_client_enable="YES"
> nfs_server_enable="YES"
> rpcbind_enable="YES"
> rpc_lockd_enable="YES"
> rpc_statd_enable="YES"
> nfs_server_flags="-u -t -n 16"
> and on the Linux client I have been trying various options to no avail.
> The mount works, but on a straight up write to the FreeBSD server,
> everything is very bursty.  I noticed this (I think) a few months ago
> where Linux dumps across an nfs mount seemed to take a lot longer and
> were getting very bursty.
> It seems if there are a mixture of reads and writes, everything is
> pretty fast. But if a client is just writing to the server, something,
> somewhere is blocking.  Doing something simple like
> ls -l /nfsmount
> from the client "wakes" up the server/client so that write stream can
> keep going. Otherwise, it will do a big blast of writes and then several
> seconds of pausing on the dump.

Looks like you're using ZFS.

Most probably that's the cause. NFS requires frequent syncs, and ZFS
respects those, becoming slow, being unable to take advantage of the ZIL.

you can find more details here:

in the NFS tuning section.

If you're not using ZFS I don't have an idea right away what your
problem could be.

Guido Falsi <mad at>

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