Shulou(Shulou.com)06/02 Report--

Author profile: Zheng Minxian, working in Nuoyun Information System (Shanghai) Co., Ltd., as a pre-sales engineer. Engaged in SDN, white box switches and other open network products to promote the work.

Upgrading the server interface from 10G to 25G brings many benefits, such as:

● Ethernet performance is 2.5 times that of 10G interface;

● Can provide higher port density for servers;

● Lower power consumption per GB of data transmission (saving electricity);

……

While these benefits are tempting, there are still a few aspects to note:

Ensure that you understand the meaning of 25G/100G

The transmission rate of Ethernet interfaces has increased roughly linearly over the past few decades (10 times every decade). Everyone's desktop computer or laptop wired network card is basically gigabit network card. In many data centers today, the server interface is 10Gbps(10 Gigabit) and the inter-switch interface is 40Gbps(40 Gigabit), and most of them are considering (or are) upgrading the network to the next generation of 25G/100G networks (the server interface is 25Gbps, and the inter-switch interconnect interface is 100Gbps).

A 100Gbps connection can be broken down into four lanes (25Gbps each) by a Break-out Cable, so 100G networks are sometimes referred to as 25G/100G networks. Similarly, 10G networks are sometimes referred to as 10G/40G networks.

10G/40G networks:

40Gbps link between Spine switch and Leaf (TOR) switch

Server interface is 10Gbps,

Different Leaf switches may have different ways of providing 10G interfaces and port densities.

1)Take a Leaf switch as an example. The port specification of the switch is: 4810Gbps+640Gbps. At this time, the 10G interface provided by the Leaf switch is the native 10G interface of the Leaf switch:

2)Take a Leaf switch as an example, the port specification of the switch is: 3240Gbps. At this time, the 10G interface provided by the Leaf switch is tapped from its native 40G interface through a one-to-four Break-out cable (in the scenario where 6 ports are used to connect to the Spine switch, it can provide (32-6)4=104 10G ports):

25G/100G networks:

● 100Gbps link between Spine switch and Leaf switch

● Server interface is 25Gbps

Different Leaf switches provide 25G interfaces in different ways and port density may be different:

1)Take a Leaf switch as an example. The port specification of the switch is: 4825Gbps+6100Gbps. At this time, the 25G interface provided by the Leaf switch is the native 25G interface of the Leaf switch:

2)Take a Leaf switch as an example, the port specification of the switch is: 32100Gbps. At this time, the 25G interface provided by the Leaf switch is tapped from its native 100G interface through a one-to-four Break-out cable (in the scenario where 6 ports are used to connect to the Spine switch, it can provide (32-6)4=104 25G ports):

II. Considering whether upgrading is needed based on the scale of business expansion

For some leading enterprises, upgrading from the current 10/40G network to 25/100G is the fastest way. After all, it can take years to plan, build, and bring a data center online. (Taking too long means you risk being overtaken by competitors.) The world's major public cloud giants are basically American enterprises, paying special attention to some of the leaders in order to maintain (or even to expand the lead), even if the 25G/100G equipment, optical modules, etc. are much more expensive than today, but they still gradually upgrade the existing data center network from 10/40G to 25/100G a few times ago (of course, they also built some new data centers in the same period).

▲ Forecast of the number of optical modules shipped to Amazon, Google and Microsoft

Looking at the shipments of the entire optical module market, it will be found that each new optical module has not been widely used for one or two years. Think about it too, after all, just launched that period of time the price is very expensive. In the past few years, the application of 25G/100G in China is later than that of several major OTTs in the United States, and most of the domestic 25G/100G are used in newly built data centers. Today (2018), many of the 10G data centers in China are about to face network bottlenecks or the design life of IT equipment. The price of 25G/100G optical modules is much lower than that of the previous two years. Switching to 25G is a good choice (economy + performance improvement).

▲ Shipments forecast for the entire optical module market

Not every server needs to be upgraded.

If some servers in your data center don't have bottlenecks on their 10G network (or some time in the future), upgrading their network to 25G won't result in a performance boost. In this case, these servers can continue to use the 10G network and upgrade when the network is about to become a bottleneck.

Try not to purchase 40Gbps network cards

In the past few years, the number of 40G server network cards shipped has not been much. The price screenshot of the 25G and 40G server network cards of an e-commerce platform is as follows (excluding the optical module), and you can see that the prices of the two are very close.

However, 40G network cards usually do not take full advantage of the server PCIe bus. Because many servers have PCIe 3.0 x 8(Gen3 x8) slots, they can deliver 56Gbps bandwidth. Plugging an NIC with two 25G ports into a 56Gbps PCIe slot can result in higher efficiency in network-to-server performance (versus a NIC with one 40G port).

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