SAN (Storage attached network), or storage area networks

Nas and San are both competitive and cooperative, and many of the back-end storage of high-end Nas is SAN. The integration of NAS and SAN is also a trend for storage devices, such as EMC's new product VNX series .

There are a lot of things that can be listed about the difference between Nas and SAN. such as bandwidth size, distance, share advantages and disadvantages and so on. Almost all of the differences are derived from two factors. One is FC and Ethernet, the other is block and file system. In short, if the user needs to access the block via FC, the SAN is used, and if the file system needs to be accessed via Ethernet, the NAS is used.

In addition to NAS and Sans, there is a class of storage devices that are often mentioned. That's Das (direct attached Storage), which is "direct-attached storage." "Direct Connect" means that there is no FC network between the server and the storage device, but directly connected. For example, the personal computer we all know is Das, because the disk is connected directly to the motherboard. Das has been around for many years, and even today is the ideal choice for many servers. But it's a lot of problems, and it's not keeping up with it technology, like the development of virtualization. Here are a few examples:

1. Manageability is poor: Each server uses its own storage, optical hardware monitoring and maintenance will take a lot of time. If you have to do disaster recovery or backup, it's a nightmare for administrators.

2. Poor scalability: At the end of the server installation, if you find that the storage space allocation is too large, it creates a waste. If you find that there is not enough space, it can be cumbersome to scale.

3. Not keeping up with it trends, such as advanced features such as VMware Vmotion are not supported.

SAN addresses these issues. Because it provides both unified storage and a network at the same time. Uniformity and networking offer a number of benefits to the SAN:

1. Manageability: A single SAN is unified to provide storage for multiple servers. Whether it's hardware monitoring or maintenance, or disaster-tolerant backup of data, it's all done on the SAN. Make storage management easier.

2. Scalability: At the physical level, sans support hundreds of disks (such as EMC's CX4 can support 960 disks), providing a huge amount of storage space. At the logical level, this massive amount of space can be partitioned into LUNs of different sizes and allocated to the server as needed. LUNs are logical devices, so it's easy to scale or migrate.

3. In line with it trends: for example, there is good support for the hottest virtualization.

Of course, in addition to solving these problems with Das, the SAN has other distinct advantages:

1. High performance:

A. SAN better supports raid because it has more hard drives and stronger controllers. Shows the fundamentals of RAID0 for performance gains: When a chunk of data is written to a raid group, it can be divided into small chunks and written to several disks. It's like having a batch of files that need to be typed into a computer, and a manager can type a person for 5 days. Share it with 5 employees, and you can finish it in one day. We will explain in detail later when analyzing NAS performance.

B. The SAN has a larger cache. For example, CX4 's write cache can reach 10.7 GB. The cache also has a significant effect on performance, and we'll explain later when we analyze NAS performance.

2. More stable: multi-head, hot spare, multi-path mechanism to eliminate single point of failure.

3. More secure: Unified disaster recovery, backup and remote replication ensure data security.

There are also many new technologies, such as Vnx's Fastcache and FASTVP.