You cannot share a
dbPath with multiple active
mongod processes - each process requires exclusive access to the data files.
For data redundancy and readonly copies of data, MongoDB supports replica set deployments. A replica set elects a single primary member that accepts writes and can have multiple read-only secondary members. By default all reads and writes are directed to the current primary in a replica set, but your driver or application can use read preferences to read from secondary members. In the event the current primary is unavailable, replica sets also support failover based on your configuration.
However, shared storage is not ideal for a replica set as you will be writing many copies of the same data to the shared storage (which presumably also has some built-in write redundancy).
With or without replication, you should configure MongoDB's Role-Based Access Control (RBAC) so that your applications authenticate with appropriate privileges such as read-only access. The MongoDB Security Checklist has a list of security measures to consider. Even if access is limited to a trusted network, use of RBAC limits your exposure to accidental data modification and provides some audit trail in the MongoDB server logs.