Why datacenter migration needs a large two-tier network

Datacenter migration, before starting, first to be clear, the second tier network is basically a data center scene, because it is actually to solve the data center of the server virtualization after the virtual machine dynamic migration of this specific requirements appeared. For ordinary campus network and other networks, large two-level network has no special value and significance (except for some special scenarios, such as WIFI roaming and so on).

Therefore, what we call "big two level network" usually refers to the big two level network of data center.
Traditional data center network architecture
We see that the network architecture is the same as the network architecture, such as the park network, which is equivalent to the "franchise" form in the retail industry, and the "three layer to edge" architecture corresponding to it, and the "big second tier" architecture we have to talk about as "straight shop".
The use of this network architecture is because the architecture is very mature, the related two or three layer network technology (two layers of VLAN+xSTP, three layer routing) are mature technology, can be easily deployed, and also meet the data center partition module business characteristics.
But this network architecture is actually a weakness for data center. What is it? And let me sell it. I'll talk about it later.
Server virtualization trend
Because the utilization rate of traditional data center servers is too low, averaging only 10%~15%, which wastes a lot of electric energy and computer room resources. So there is a server virtualization technology.
Server virtualization technology is to dump a physical server into multiple logical servers, which are called virtual machines (VM), each VM can run independently, with its own OS, APP, and its own independent MAC address and IP address, which are via the virtual switch (vSwitch) inside the server and outside. An entity network connection.
Through server virtualization, it can effectively improve the utilization of the server, reduce the energy consumption and reduce the customer's operation and maintenance costs, so the virtualization technology has been widely used. As for why these advantages, I will not bother to say it. If you are interested, you can ask yourself "Du Niang". In short, server virtualization is a good thing.
PS:VMware is a market leading product and innovative brand in the field of server virtualization, providing a complete set of software for VM solution. Besides VMware, there are servers virtualization software such as Microsoft Hyper-V and Xen.
Virtual machine dynamic migration
After drinking, we go back to the data center network.
Actually, server virtualization has no special impact on the data center network. It is that the size of the host is bigger. (a physical server is a host, now each VM is a host), or it can be connected by two or three layers of network architecture. Some two layer fields are all right.
But after server virtualization, it brings a associated technology, which is dynamic migration of virtual machines, which brings a lot of trouble to the traditional data center network. Of course, before we talk about trouble, we have to figure out what the virtual machine dynamic migration is.
The so-called virtual machine dynamic migration is the process of moving a virtual machine system from one physical server to another at the same time that the service is running normally on a virtual machine. The process is unaware for the end user, enabling the administrator to deploy the server resources flexibly, or to maintain and upgrade the physical server without affecting the user's normal use.
As a matter of fact, the dynamic migration is to move the virtual machine, but when the move is required, the service running on the virtual machine will not be interrupted, and the users outside are not aware of it.
To figure out what is the virtual machine's dynamic migration, let's see what the technology brings to the network.