Difference Between NAS/DAS/SAN

Difference Between NAS/DAS/SAN

NAS vs. DAS

The key difference between direct-attached storage (DAS) and NAS is that DAS is simply an extension to an existing server and is not necessarily networked. NAS is designed as an easy and self-contained solution for sharing files over the network.

Both DAS and NAS can potentially increase availability of data by using RAID or clustering.

When both are served over the network, NAS could have better performance than DAS, because the NAS device can be tuned precisely for file serving which is less likely to happen on a server responsible for other processing. Both NAS and DAS can have various amount of cache memory, which greatly affects performance. When comparing use of NAS with use of local (non-networked) DAS, the performance of NAS depends mainly on the speed of and congestion on the network.

NAS is generally not as customizable in terms of hardware (CPU, memory, storage components) or software (extensions, plug-ins, additional protocols) as a general-purpose server supplied with DAS.

NAS vs. SAN[edit]

Visual differentiation of NAS vs. SANuse in network architecture

NAS provides both storage and a file system. This is often contrasted with SAN (Storage Area Network), which provides only block-based storage and leaves file system concerns on the "client" side. SAN protocols include Fibre Channel, iSCSI, ATA over Ethernet (AoE) andHyperSCSI.

One way to loosely conceptualize the difference between a NAS and a SAN is that NAS appears to the client OS (operating system) as a file server (the client can map network drives to shares on that server) whereas a disk available through a SAN still appears to the client OS as a disk, visible in disk and volume management utilities (along with client's local disks), and available to be formatted with a file system and mounted.

Despite their differences, SAN and NAS are not mutually exclusive, and may be combined as a SAN-NAS hybrid, offering both file-level protocols (NAS) and block-level protocols (SAN) from the same system. An example of this is Openfiler, a free software product running on Linux-based systems. A shared disk file system can also be run on top of a SAN to provide filesystem services.

NDMP, or Network Data Management Protocol, is a protocol invented by the NetApp and Legato companies, meant to transport data between network attached storage (NAS) devices and backup devices. This removes the need for transporting the data through the backup server itself, thus enhancing speed and removing load from the backup server.

Most contemporary commercial, multi-platform backup software, such as Bacula, Amanda, CA ARCserve, EMC NetWorker, EMC Avamar, Symantec NetBackup, Backup Exec (since v11d), CommVault Simpana, Virtos S.O.S Backup, IBM Tivoli Storage Manager, Hitachi Data Systems (HDS), Dell Software NetVault Backup, Syncsort DPX, Zmanda, HP Data Protector and others support this protocol.