You can use the Volume Replication with the NFS Auto Failover, make sure that you have NFS Auto Failover feature, this is offered with the TRIAL version for 60 days or you can purchase this from our website.
Make sure that when you create the NAS volume that you enable the Replication for the NAS volume for reach of the DSS V6 servers and assign one as the Source and the other as the Destination.
If you do not have enough storage capacity to create a Snapshot then you will need to add more storage or remove the NAS volume and resize to allow the creation for the Snapshot volume to be assigned to the NAS volume for the Data Replication.