Using NFSv4

Support for NFSv4

Data ONTAP supports all of the mandatory functionality in NFSv4, except the SPKM3 and LIPKEY security mechanisms, including the following:

COMPOUND--Allows a client to request multiple file operations in a single remote procedure call (RPC) request.
Pseudo-fs--Used by NFSv4 servers to determine mount points on the filer. There is no mount protocol in NFSv4.
Locking--Lease-based. There are no separate Network Lock Manager (NLM) or Network Status Monitor (NSM) protocols in NFSv4.
Named attributes--Similar to Windows NT streams.

Limitations for NFSv4

Be aware of the following limitations when using NFSv4 with Data ONTAP:

Delegations, which allow the NFS server to delegate the handling of files to the client, are not supported.
Named attributes can only be created if CIFS is running on the filer.
Names with non-ASCII characters on volumes other than UTF8 volumes are rejected by the filer.
All file handles are persistent. The server does not give out volatile file handles.
Migration and replication are not supported.
NFSv4 access control lists (ACLs) are not supported. ACLs set by CIFS apply to NFSv4 access, as they do for other versions of NFS.
All recommended attributes are supported, except for the following:
- acl
- aclsupport
- archive
- hidden
- homogeneous
- mimetype
- quota_avail_hard
- quota_avail_soft
- quota_used
- system
- time_backup
NFSv4 does not use the User Datagram Protocol (UDP) transport protocol. If you enable NFSv4 and disable NFS over TCP by setting options nfs.tcp.enable to Off, then NFSv4 is effectively disabled.

How the pseudo-fs in NFSv4 affects mount points

NFSv4 uses a pseudo-fs as an entry point into the filer for determining mount points. A pseudo-fs allows you to use one port for security, rather than several. All NFSv4 servers support the use of a pseudo-fs.

You may experience inconsistencies with mount points between NFSv3 and NFSv4, because of the pseudo-fs used in NFSv4.

In the examples that follow, you have these volumes:

/vol/vol0 (root)
/vol/vol1
/vol/home

Example 1

In NFSv3 if you do not use the complete path from /vol/vol0, and you mount filer:/, the mount point is filer:/vol/vol0. That is, if the path does not begin with /vol in NFSv3, then Data ONTAP adds /vol/vol0 to the beginning of the path.

In NFSv4, if you do not use the complete path from /vol/vol0 and you mount filer:/, you mount the root of the pseudo-fs and not /vol/vol0. Data ONTAP does not add /vol/vol0 to the beginning of the path.

Therefore, if you mount filer:/ /n/filer using NFSv3 and try the same mount using NFSv4, you would mount a different file system.

Example 2

In Data ONTAP's implementation of the NFSv4 pseudo-fs, the nodes "/" and "/vol" are always present and form the common prefix of any reference into the pseudo-fs. Any reference that does not begin with "/vol" is invalid.

In this example, there is a /vol/vol0/home directory. In NFSv3, if you mount filer:/home /users, /home is considered as the directory /vol/vol0/home. In NFSv4, if you mount filer:/home /users, /home is not considered as the volume /vol/home; it is considered an invalid path in the pseudo-fs tree.

Specifying the user ID domain for NFSv4

The domain that Data ONTAP uses for NFSv4 user ID mapping by default is the NIS domain, if one is set. If a NIS domain is not set, the DNS domain is used. You might need to set the user ID domain if, for example, you have multiple user ID domains.

To specify the user ID domain to be used for NFSv4 user ID mapping, complete the following step.

Step	Action
1	Enter the following command: option nfs.v4.id_domain domain