NAS (Network Attached Storage)
A third type of storage solution exists that is a hybrid option called Network Attached Storage (NAS). This solution uses a dedicated server or “appliance” to serve the storage array. The storage can be commonly shared to multiple clients at the same time across the existing Ethernet network. The main difference between NAS and DAS and SAN is that NAS servers utilize file level transfers, while DAS and SAN solutions use block level transfers which are more efficient.
NAS storage typically has a lower startup cost because the existing network can be used. This can be very attractive to small-to-medium size businesses. Different protocols can be used for file sharing such as NFS for UNIX clients and CIF for Windows clients. Most NAS models implement the storage arrays as iSCSI targets that can be shared across the networks. Dedicated iSCSI networks can also be configured to maximize the network throughput. The following diagram shows how a NAS configuration might look.