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Sep 07, 2017



1.Direct Attached Storage (DAS)

The storage device is directly connected to the server via a cable (usually a SCSI interface cable). I / O requests are sent directly to the storage device. This way is to connect a single or two small clusters of servers.

It is characterized by the initial cost may be relatively low. However, for this type of connection, for each server or multiple PC environment, each PC or server has its own storage disk, capacity redistribution difficult; for the entire environment of the storage system management, work cumbersome and repeat, There is no centralized management solution. So the overall management costs are higher.

PC in the disk or only one external SCSI interface JBOD belong to the DAS architecture.

2. Network Attached Storage (NAS)

NAS devices are typically integrated with a processor and a disk / disk enclosure, similar to a file server. Connect to a TCP / IP network (via LAN or WAN) to access data via a file access protocol (eg NFS, CIFS, etc.).

The NAS translates the file access request into an internal I / O request. In this way, the storage device is connected to an IP-based network. Unlike the DAS and SAN, the server sends a file access request to the storage device NAS through the "File I / O" mode. NAS is generally installed with its own operating system, it will File I / O into Block I / O, sent to the internal disk.

NAS systems have lower cost and easy file sharing. But because it is a file request, the performance of the device compared to the block request is poor; and the NAS system is not suitable for systems that do not use the file system for storage management, such as some databases.

NAS must be able to access volumes or physical disks. NAS must have the ability to access Ethernet, that is, must have an Ethernet card.


If the SAN is based on a TCP / IP network, implement an IP-SAN network. This is the server and storage devices through a dedicated network connection, the server through the "Block I / O" to send data access requests to the storage device.

The most commonly used is the iSCSI technology, that is, the SCSI command packet in the TCP / IP packet transmission, that is, SCSI over TCP / IP.

The advantages of IP SAN are:

The use of ubiquitous Ethernet network, to a certain extent, to protect the existing investment.

IP storage beyond the geographical distance of the restrictions, suitable for remote backup of critical data.

IP network technology is mature, there is no interoperability problem

IP storage reduces the complexity of configuration, maintenance, and management.

IP networks have been widely recognized by the IT industry - network management software and services products available

The widespread use of Gigabit networks greatly improves the performance of IP networks

The development of 10 Gigabit network technology, so that IP storage performance can go beyond FC storage

4. Storage Area Network (FC SAN)

Storage devices form a separate network, most of the use of fiber connections, using Fiber Channel (Fiber Channel, referred to as FC). Server and storage devices can be any connection, I / O requests are sent directly to the storage device.

Fiber Channel protocol actually solves the underlying transport protocol, and the high-level protocol still uses the SCSI protocol, so the Fiber Channel protocol can actually be seen as SCSI over FC.

The advantages of the storage area network are as follows:

Server and storage devices farther away (Fiber Channel network: 10 km compared to DAS SCSI: 25 m);

High reliability and high performance;

Multiple servers and storage devices can be connected arbitrarily

Centralized storage devices replace multiple independent storage devices to support storage capacity sharing;

Through the corresponding software makes the storage device on the SAN performance as a whole, so there is a high degree of scalability;

Data sharing can be provided by software centrally managing and controlling storage devices on a SAN

Because SANs are typically Fiber Channel-based solutions, dedicated Fiber Channel switches and management software are required to cost the SAN at a higher cost than DAS and NAS.

Comparison of SAN and NAS:

1, NAS equipment can generally provide a variety of protocol access data, and SAN can only use the SCSI protocol to access.

2, NAS can be in a disk array to achieve multiple client shared access, including the simultaneous access to a directory or file. In the SAN mode, unless all clients have a dedicated cluster management system or cluster file system module, you can not share a LUN, and the forced sharing will destroy the data.

Performance: FC performance best, single port can reach 2Gbps bandwidth; NAS performance is the worst, even with Gigabit network, usually only 30-40MBps; single Gigabit iSCSI can reach 60-70MBps; 10G network, single 10 trillion mouth speed can be more than 500MBps.

Scalability: FC and iSCSI architecture with SAN, the best scalability in the storage network, easy to increase the user or increase the storage module.

Application cost: FC application cost is the highest, need to support the expensive optical switch (8 port fiber switch about 3-4 million); each server needs with fiber channel card (fiber channel card 5000-1 million); and (8-port Gigabit switch 1000 yuan); the server itself with Gigabit Ethernet port, even if the increase is a network card is 500 yuan, the use of ordinary ultra-five (Figure), the use of fiber-optic medium; Line can be, the price can be ignored;

Market positioning: FC occupy high-end, iSCSI in the high-end, NAS and DAS at the low end

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