Direct Attached Storage (DAS)are storage devices that are directly connected to the servers. Servers connect to these devices using high speed interconnects such as SCSI (Small Computer System Interface). The issue with DAS is that the storage utilization is low (on the average 50%) and space cannot be pooled, making management and maintenance difficult.

Network Attached Storage (NAS)is a server that is dedicated to file sharing. It allows hard disk storage space to be added to a network without having to bring down these servers and allows the servers and workstations on the network to access this storage at a file level.

Storage-Area Network (SAN)is a dedicated network that connects all the servers and clients to a shared pool of storage. The pool consists of servers, external storage devices, switches, and network and storage management tools.

SANs increase the availability of data by allowing servers on the network to access any storage device on the SAN. Server performance is also increased, as storage-intensive processes such as backup and recovery are off-loaded to the SAN. SANs also lower cost-of-ownership through centralized management.

Additionally, SAN addresses two fundamental NAS issues. First, there are applications such as databases that need a “block level” access to storage as opposed to a file level access, and second that the increased network traffic from servers to storage can cause congestion on local network. SAN allows a block level access to storage and since it has its own dedicated network, server-storage traffic does not impact the local network.

NAS and SAN are complimentary solutions in the sense that NAS servers can use a SAN for their storage. Application servers access files on a NAS server and in turn NAS servers use the block level services on a SAN for their storage.

Technology Information

iSCSI White Paper

RAID White Paper