After upgrading to Veeam Backup & Replication U4, Veeam vPower NFS datastore location might be changed.
The NFS datastore path having changed is a known issue in the Veeam Backup & Replication U4. Starting with Update 4, the disk with the largest capacity is selected by default to be used as the NFS datastore location.
Review each Repository's Mount Server settings and adjust the "Instant recovery write cache folder" as needed.
If the IRCache path specified is invalid, it may cause the upgrade error documented in KB4166.
"Error 1327. Invalid Drive: [a-z]:\"