Shulou(Shulou.com)06/03 Report--

1. NAS

Network storage device (Network Attached Storage,NAS) is the name of a special data storage technology, which can be directly connected to the computer network and provides centralized data access services for users of different operating systems.

Advantages of NAS: NAS devices generally support multi-computer platforms, and users can access the same documents through network support protocols, so NAS devices can be used in hybrid Unix/Windows NT Lans without modification.

Disadvantages of NAS: NAS does not address a key issue related to the file server, even if the bandwidth consumption in the process is used. Unlike storage area networks (SAN) that move data streams out of LAN, NAS still uses the network for backup and recovery. One disadvantage of NAS is that it transfers storage transactions from parallel SCSI connections to the network. This means that LAN must handle storage disk requests that include backup operations in addition to normal end-user transport streams.

II. DAS

Direct attached Storage (Direct Attached Storage,DAS) is a directly attached storage that connects a storage device directly to a computer through a SCSI interface or fibre Channel. The applicable environments for DAS are:

1. Servers are geographically dispersed, and it is very difficult to interconnect them through SAN or NAS.

2. When the storage system must be connected directly to the application server (such as Microsoft Cluster Server or the "original partition" used by some databases)

3. There is only a single server, and the storage device does not need to be shared with other servers.

III. SAN

Storage area network (Storage Area Network,SAN) means that the storage is allocated to different servers through the fiber switch, the server provides services through Ethernet, and the storage area is isolated from the application area of the user.

SAN (Storage area Network) is connected to a group of computers via fibre Channel. Multi-host connectivity is provided in this network, but not through a standard network topology.

High bandwidth: the structure of SAN allows any server to connect to any storage array, so that no matter where the data is placed, the server can directly access the required data. Because of the optical fiber interface, SAN also has higher bandwidth.

Independent storage network: because the SAN solution strips storage functions from basic functions, running backup operations does not need to consider their impact on the overall performance of the network.

Ease of management: the SAN solution also simplifies management and centralized control, especially when all storage devices are clustered together.

Remote deployment: the optical interface provides a connection length of 50 kilometers, which makes it very easy to achieve physically separate storage that is not in the computer room.

SAN is mainly used in the working environment with large storage capacity, such as ISP, bank and so on. The biggest disadvantage is the high cost.

IV. Summary of differences:

According to the different characteristics of DAS, NAS and SAN, DAS and SAN are disk allocation based on storage space, which is based on the storage mode at the hardware level, while NAS is based on the storage mode at the application level, which can be summarized according to the application environment.

DAS mostly uses SCSI or SAS interface. Due to the singleness and high performance of deployment nodes, it is suitable for enterprise applications with a single node or servers with scattered geographical locations. DAS is currently being used less and less due to deployment limitations.

NAS uses the existing Ethernet network, so the deployment is flexible and the cost of deployment is very low. The characteristics based on TCP/IP protocol can provide rich network services and provide data storage and backup in the form of files. However, TCP/IP protocol determines that the data packaging and unpacking of data transmission will take up system resources. In addition, the transmission rate is limited by the speed of Ethernet, so it is not suitable for enterprise applications. It is usually deployed in departmental applications.

SAN storage uses optical fiber network for transmission, and is independent of the application network, and can provide very high bandwidth. Data transmission is based on block protocol, so it can be transmitted directly without data processing, so its performance is the best. In addition, optical fiber lines can provide long-distance high-bandwidth links, which can achieve remote disaster recovery applications in data centers, but the deployment cost is high. Therefore, SAN storage is mostly used in enterprise storage deployment.

With the development of technology, the IP SAN technology of iSCSI technology makes NAS storage seize a part of the market share of SAN storage. In addition, with the development of 10Gb Ethernet technology, the development space of NAS storage will be broader.

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