NetWorker: Disk devices unmounting intermittently

• Intermittent unmounting of disk-based devices with errors:
  nsrd NSR warning: Operation on device 'device' failed: cannot read adv_file label: Resource temporarily unavailable
nsrd NSR info media warning: device opening: Cannot read identifier for device 'device': Resource temporarily unavailable 

• Saves already in progress proceed and complete.
• New saves are rejected Device requires manual remounting.

This issue may be caused by using NFS shares as Advanced File Device paths used by many Client Direct backups concurrently.

During each save operation, an NFS mount is performed in the background to accommodate Client Direct and traditional Storage Node-based backups. Too many clients using the same path concurrently can overwhelm the host in some cases, causing it to reject further connections.

To address the root cause, review the NFS and OS configuration for the export host limitations with its NFS exports.

From a NetWorker standpoint - spreading the devices between different NFS mounts can help alleviate the condition on the host.