NFS V4 export considerations

For information on NFS V4, refer to NFS Version 4 Protocol and other information found in the Network File System Version 4 (nfsv4) section of the IETF Datatracker website.

To export a GPFS™ file system using NFS V4, there are two file system settings that must be in effect. These attributes can be queried using the mmlsfs command, and set using the mmcrfs and mmchfs commands.

The -D nfs4 flag is required. Conventional NFS access would not be blocked by concurrent file system reads or writes (this is the POSIX semantic). NFS V4 however, not only allows for its requests to block if conflicting activity is happening, it insists on it. Since this is an NFS V4 specific requirement, it must be set before exporting a file system.
```
flag value          description
---- -------------- -----------------------------------------------------
 -D nfs4            File locking semantics in effect
```
The -k nfs4 or -k all flag is required. Initially, a file system has the -k posix setting, and only traditional GPFS ACLs are allowed. To export a file system using NFS V4, NFS V4 ACLs must be enabled. Since NFS V4 ACLs are vastly different and affect several characteristics of the file system objects (directories and individual files), they must be explicitly enabled. This is done either exclusively, by specifying -k nfs4, or by allowing all ACL types to be stored.
```
flag value          description
---- -------------- -----------------------------------------------------
 -k  all            ACL semantics in effect
```

Note: In IBM Spectrum Scale™ 4.2 release, NFS connections are limited to a maximum of 2250 for a large number of NFS exports. The maximum number of NFS exports supported is 1000.