The Concept of Root Squash: In the world of NFS, 'Root Squashing' is a fundamental security feature. By default, most modern storage systems (including FlashArray File Services) do not trust the 'root' user of a remote client. This prevents a user with administrative access on a random laptop or server from gaining full administrative control over the files on the central storage.

Mounting vs. Accessing:

Mounting: This is the process of attaching the remote export to the local file system. If the Export Policy allows the client IP to connect, the mount will succeed.

Accessing: Once mounted, the array evaluates the identity of the user. If Root Squash is enabled, the array 'squashes' the root user (UID 0) and maps it to a non-privileged user (usually nobody or anonymous). Consequently, the client's root user loses their administrative permissions when trying to read/write files.

The Export Policy Setting: The behavior described (able to mount but permission denied for files as root) is almost always caused by the User ID Mapping or Access rules within the Export Policy.

To resolve this, an administrator must edit the specific rule in the Export Policy and enable 'No Root Squash' (or change the mapping to allow root access). This tells the FlashArray to honor the client's root identity.

Why Options A and B are incorrect:

Managed Directory: This is where you set the directory structure and quotas, but it doesn't control the protocol-level identity mapping.

File System: While a file system has underlying permissions, if the mount is successful but specifically blocks the root user, the 'gatekeeper' is the Export Policy rule.