Nutanix Volumes allows administrators to provision a volume group with one or more volumes that can be attached to multiple VMs or physical servers via iSCSI. This enables the creation of a Microsoft Server Failover Cluster that uses shared storage for a critical application. The volume group can be attached to VMs running on an AHV-hosted cluster and bare metal servers for maximum resiliency1. Reference: Nutanix Volumes Administration Guide1

The Files feature that the administrator should enable to ensure the sessions will auto-reconnect in such events is Durable File Handles. Durable File Handles is a feature that allows SMB clients to reconnect to a file server after a temporary network disruption or a client sleep state without losing the handle to the open file. Durable File Handles can improve the user experience and reduce the risk of data loss or corruption. Durable File Handles can be enabled for each share in the Files Console. Reference: Nutanix Files Administration Guide, page 76; Nutanix Files Solution Guide, page 10

Nutanix Volumes is a feature that allows users to create and manage block storage devices (volume groups) on a Nutanix cluster. Volume groups can be accessed by external hosts using the iSCSI protocol. To secure volume groups from unauthorized access, Nutanix recommends configuring CHAP (Challenge-Handshake Authentication Protocol) for each volume group in Prism Element. CHAP is a security feature that authenticates iSCSI initiators and targets before allowing access to a volume group. CHAP requires both the initiator and the target to have a shared secret (a password) that is used to generate a challenge and a response during the authentication process. CHAP can prevent unauthorized access to volume groups and protect data from malicious attacks. Reference: Nutanix Volumes Administration Guide, page 25; Nutanix Volumes Security Guide

The component that must first be upgraded to a compatible version before upgrading Files or creating a file server is Prism Central. Prism Central is a web-based user interface that allows administrators to manage multiple Nutanix clusters and services, including Files. Prism Central must be upgraded to a compatible version with Files before upgrading an existing file server or creating a new file server. Otherwise, the upgrade or creation process may fail or cause unexpected errors. Reference: Nutanix Files Administration Guide, page 21; Nutanix Files Upgrade Guide

The most likely cause for this issue is that the file server resides on a single node cluster. A distributed share is a type of SMB share or NFS export that distributes the hosting of top-level directories across multiple FSVMs, which improves load balancing and performance. A distributed share cannot be created on a single node cluster, because there is only one FSVM available. A distributed share requires at least two nodes in the cluster to distribute the directories. Therefore, the option to use distributed share/export type instead of standard is not present when creating a share on a single node cluster. Reference: Nutanix Files Administration Guide, page 33; Nutanix Files Solution Guide, page 8