DSM presents a logical view of shared memory, thus implements the necessary communication and maintains consistency for the application. Typically, users within a DSM will each have their own local cache for the sake of efficiency. DSM maintains a directory service to store complete state and location information for all data residing within the system. Files can then be shared either by replication or by migration. Replication means there must be maintanence on multiple copies of data.
Migration consists of having only one copy of it.
If a system is using it and another system is trying to access it, they will be 'locked-out' until the first system gives it up. DSM is treated a lot like data for distributed transactions is treated. Filtering Subnet because this sets up a filtering subnet outside of the internal firewall. Filtering Subnet because this sets up a filtering subnet outside of the internal firewall.