For instance, there may be one disk array to which all the servers are attached. As there is only one source, there will be no synchronisation conflicts. However, there are two main problems with this solution. Second, some storage access arbitration is required so that servers reading and writing to the array don't cause conflicts. Such arbiters are often known as distributed lock managers.
SANs provide highly reliable arbitrated storage systems on their own subnetwork.
Shared nothing clusters leave individual storage systems in the hands of the nodes. Each node has its own storage, and any data changes are mirrored across all devices. Unlike shared disks, there's no need for arbitration because each node accesses its own storage subsystem. It also provides automated backup systems, with as many copies of each data object as there are nodes in the cluster. The first and most obvious disadvantage of the shared nothing system is that it requires massive redundancy.