Manual Pages  — NFSD

When using IPv6 addresses for DSs be wary of using link local addresses. The IPv6 address for the DS is sent to the client and there is no scope zone in it. As such, a link local address may not work for a pNFS client to DS TCP connection. When parsed, nfsd will only use a link local address if it is the only address returned by getaddrinfo(3) for the DS hostname.

-m mirror_level
	This option is only meaningful when used with the -p option. It specifies the "mirror_level", which defines how many of the DSs will have a copy of a file's data storage file. The default of one implies no mirroring of data storage files on the DSs. The "mirror_level" would normally be set to 2 to enable mirroring, but can be as high as NFSDEV_MAXMIRRORS. There must be at least "mirror_level" DSs for each exported file system on the MDS, as specified in the -p option. This implies that, for the above example using "#/export1" and "#/export2", mirroring cannot be done. There would need to be two DS entries for each of "#/export1" and "#/export2" in order to support a "mirror_level" of two. If mirroring is enabled, the server must use the Flexible File layout. If mirroring is not enabled, the server will use the File layout by default, but this default can be changed to the Flexible File layout if the sysctl(1) vfs.nfsd.default_flexfile is set non-zero.
-t
	Serve TCP NFS clients.
-u
	Serve UDP NFS clients.
-e
	Ignored; included for backward compatibility.

For example, "nfsd -u -t -n 6" serves UDP and TCP transports using six daemons.

A server should run enough daemons to handle the maximum level of concurrency from its clients, typically four to six.

The nfsd utility listens for service requests at the port indicated in the NFS server specification; see Network File System Protocol Specification, RFC1094, NFS: Network File System Version 3 Protocol Specification, RFC1813, Network File System (NFS) Version 4 Protocol, RFC3530 and Network File System (NFS) Version 4 Minor Version 1 Protocol, RFC5661.

If nfsd detects that NFS is not loaded in the running kernel, it will attempt to load a loadable kernel module containing NFS support using kldload(2). If this fails, or no NFS KLD is available, nfsd will exit with an error.

If nfsd is to be run on a host with multiple interfaces or interface aliases, use of the -h option is recommended. If you do not use the option NFS may not respond to UDP packets from the same IP address they were sent to. Use of this option is also recommended when securing NFS exports on a firewalling machine such that the NFS sockets can only be accessed by the inside interface. The ipfw utility would then be used to block nfs-related packets that come in on the outside interface.

If the server has stopped servicing clients and has generated a console message like "nfsd server cache flooded...", the value for vfs.nfsd.tcphighwater needs to be increased. This should allow the server to again handle requests without a reboot. Also, you may want to consider decreasing the value for vfs.nfsd.tcpcachetimeo to several minutes (in seconds) instead of 12 hours when this occurs.

Unfortunately making vfs.nfsd.tcphighwater too large can result in the mbuf limit being reached, as indicated by a console message like "kern.ipc.nmbufs limit reached". If you cannot find values of the above sysctl values that work, you can disable the DRC cache for TCP by setting vfs.nfsd.cachetcp to 0.

The nfsd utility has to be terminated with SIGUSR1 and cannot be killed with SIGTERM or SIGQUIT. The nfsd utility needs to ignore these signals in order to stay alive as long as possible during a shutdown, otherwise loopback mounts will not be able to unmount. If you have to kill nfsd just do a "kill -USR1 <PID of master nfsd>"

If mirroring is enabled via the -m option and there are Linux clients doing NFSv4.1 mounts, those clients need to be patched to support the "tightly coupled" variant of the Flexible File layout or the sysctl(1) vfs.nfsd.flexlinuxhack must be set to one on the MDS as a workaround.