How resources become available to NFS clients

Resources that NFS clients can mount

NFS clients can mount only those resources that have been exported. An exported resource is one that you have made available for mounting.

How Data ONTAP matches mount requests with exported resources

When Data ONTAP receives a mount request from a client, it compares the path name in the mount request to the path names of the exported resources. If Data ONTAP finds a match, the NFS client can mount the resource. Data ONTAP uses the longest matching prefix in the path name in determining access restrictions.

Example

Suppose you export both the /vol/vol0/home resource and the /vol/vol0 resource. When a host tries to mount the /vol/vol0/home/user1 directory, Data ONTAP applies the access restrictions specified for the /vol/vol0/home resource to determine whether the host should be granted access. Similarly, when a host tries to mount the /vol/vol0 directory, Data ONTAP applies the access restrictions specified for the /vol/vol0 resource.

Ways to export resources

You can export resources in two ways:

Specify resources in the /etc/exports file and execute the exportfs command either at the command line or from the /etc/rc file to export the resources according to the specifications in the /etc/exports file.
This method is for exporting resources that you want to export after each filer reboot.
Use the exportfs command to export resources that are not specified in the /etc/exports file or to export resources specified in the /etc/exports file with different access restrictions.
This method is for exporting resources temporarily because the exportfs command is not persistent across filer reboots.

For information about specifying what and how resources are exported in the /etc/exports file, see How /etc/exports works. For information about how to use the exportfs command, see Exporting or unexporting resources using the exportfs command.

Rules for exporting resources

Regardless of the method for exporting a resource, remember these rules:

You must specify the complete path name for a resource to be exported. That is, the path name must begin with the /vol prefix.
You cannot export /vol, which is not a path name to a file, directory, or volume. If you want to export all volumes on the filer, you must export each volume separately.
When you export a resource to multiple targets, separate the target names with a colon (:).

About exporting different levels of a directory hierarchy

The way Data ONTAP exports a resource is similar to that used by the SunOS 4.x operating system. However, Data ONTAP enables you to export a resource whose ancestor has already been exported. For example, you can export the /vol/vol0/home/users directory after you export the /vol/vol0/home directory.

When exporting different levels of a directory hierarchy, take care not to give clients greater access permissions at a higher level in the hierarchy. For example, in the following /etc/exports file, the first entry specifies no access restrictions for the /vol/vol0 volume. That is, any host can mount the /vol/vol0 volume as read-write. The second entry restricts access to the /vol/vol0/home directory to specified hosts. However, because the first entry gives any host permission to mount the /vol/vol0 volume, hosts other than host1 and host2 can have access to the /vol/vol0/home directory by mounting the /vol/vol0 volume.

/vol/vol0

/vol/vol0/home -access=host1:host2