What is Das, NAS, San?

Direct Attached Storage-direct connection to Storage refers to the direct connection of storage devices to a computer through the SCSI interface or fiber channel. The application environment of DAS is as follows: 1) servers are geographically dispersed, it is very difficult to connect them through San or NAS (the branch of a store or bank is a typical example); 2) when the storage system must be directly connected to the Application Server (such as Microsoft Cluster Server or the "original partition" used by some databases); 3) applications, including many database applications and application servers, they need to be directly connected to the storage, and the group application and some mail services are also included.

When the servers are geographically dispersed and it is difficult to connect to each other through remote connection, direct connection to storage is a better solution or even the only solution. Another reason for the direct connection to storage is that the enterprise decides to keep the existing network system with a low transmission rate.

The emergence of NAS and San has responded to three important development trends: the network is becoming the main information processing mode; the amount of data to be stored has increased; as a strategic asset for competitive advantage, data is becoming more important.

NAS (network attached storage-network connected storage) connects storage devices to a group of computers through a standard network topology (such as Ethernet. NAS is a component-level storage method, which focuses on helping working groups and department-level organizations quickly increase storage capacity. Engineering teams that need to share large CAD documents are typical examples.

NAS products include storage devices (such as hard drive arrays, CD or DVD drives, tape drives, or removable storage media) and integrated simple servers, it can be used to implement all functions related to file access and management. The simple server is optimized to complete a series of simplified functions, such as file storage and service, email, and Internet cache. The simple server integrated into the NAS device can separate the storage functions from other functions executed by the application server.

This method improves data availability in two aspects. First, even if the corresponding application server no longer works, the data can still be read. Second, the simple server itself will not crash, because it avoids the primary cause of server crash, that is, problems caused by application software.

NAS has several notable advantages. First, NAS products are truly plug-and-play products. NAS devices generally support multiple computer platforms. Users can access the same document through the network support protocol. Therefore, NAS devices can be used in a hybrid UNIX/Windows nt lan without any need for transformation. Second, the physical location of the NAS device is also flexible. They can be placed within a working group, close to the application server in the data center, or in another location, connected to the network through a physical link. Without application server intervention, NAS devices allow users to access data on the network, which can reduce CPU overhead and significantly improve network performance.

NAS does not solve a critical problem related to the file server, that is, the bandwidth consumption during the backup process. Unlike the storage area network (SAN) that transfers backup data streams from the 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 the lan must not only process normal end user transmission streams, but also handle storage disk requests including backup operations.

A san (storage region Network) is connected to a group of computers through fiber channels. Multi-host connection is provided in the network, but not through the standard network topology.

San focuses on the unique issues of enterprise-level storage. The two root causes of the current enterprise storage solution problems are the structural limitations arising from the close integration of data and application systems, and the restrictions currently imposed by the SCSI standard for small computer systems. Most analyses regard San as an enterprise-level storage solution in the future. This is because SAN is easy to integrate, improves data availability and network performance, and reduces management tasks.

The advantages of the San solution include the following:

San provides an easy way to connect to an existing LAN and supports a wide range of SCSI and IP protocols through the same physical channel. San is not subject to the current mainstream SCSI-based storage structure layout restrictions. It is particularly important that with the explosive growth of storage capacity, SAN allows enterprises to independently increase their storage capacity.

The San structure allows any server to connect to any storage array, so that no matter where the data is stored, the server can directly access the required data. Because the optical fiber interface is used, San also has higher bandwidth.

Because the San solution separates the storage from basic functions, you do not need to consider the impact of the San solution on the overall network performance when running backup operations. The San solution simplifies management and centralized control, especially when all storage devices are clustered together. Finally, the optical fiber interface provides a connection length of 10 kilometers, which makes it easy to physically separate and store data outside the data center.

San is mainly used in work environments with large storage capacity, such as ISP and bank. problems such as high costs and undefined standards affect the San market. However, as the business volume of these users increases, san also has broad application prospects.