Data Center Network Architectures and Research Problems

Data centers have progressively become an essential part of Internet services and networking.  This has resulted in setting key demands for the current data center network architecture. Demands like support for cloud computing, competence, scalability and efficiency results in appealing confronts from network architecture’s perspective. Like other sciences, research in data centers is essential to keep the center running smoothly.  Research projects must be paid keen attention for the purpose of quick improvement. Agility is the key. The more agile a data-center network is, the more efficient the deployment of money and resources is. During the research process there is a whole gamut of challenges. The major ones include – formulating ideas, setting out detailed designs to code up and implement, bringing together all the equipment to run the experiments and make them real.

There are several research problems or hitches in data center. Some of them are enlisted below:

Cost:

It is essential to understand the cost structure in a data center. There are various components in a data center which eat up the costs. Some components include – Servers, Infrastructure, Electrical utility costs and lastly the Network (Links, transit, equipment). Power associated expenses are similar to the networks. IT devices consume 59% of each watt brought, 8% to delivery losses and 33% for cooling purposes. Cooling costs could be brought down by permitting the data centers to run hotter, which may need the network to be more flexible in nature. Important fraction of network related costs is spent on networking equipment. Other fraction of the total costs of the network recount to wide area networking that includes traffic to end users, traffic between data centers and regional services.

Cloud Servicing:

Data centers supporting cloud services vary from distinctive enterprise data centers. Cloud service data centers need automation, unlike enterprise data center where automation is inequitable. Cloud service data centers support large economies of scale. Scaling out dispense workload to small cost hardware, in contrast to updating lofty cost hardware. The enterprise networking architectures were initially developed for much smaller data centers, in contrast to the ones active today. The limitations of the conventional architecture have resulted in quite a few workarounds and squares for the protocols to keep up with the new anxieties on data centers.

Unnecessary subscription of resource and fragmentation:

Unnecessary subscription ratio means the ratio of subscriptions to what is offered restricted server-to-server capacity limits the data center capacity and fragments the server pool. This is because idle resources cannot be allotted where they it is required. To evade this trouble all applications should be placed carefully also taking the impact of the traffic into consideration.  However, in practice this is challenging. Partial server-to-server capacity guides to designers clustering the servers around one another in the ladder, because the distance in the ladder influences the performance and cost of the communication

Reliability, utilization and fault tolerance:

Data centers undergo pitiable reliability and utilization. In case some component of the data center is unsuccessful, there must be some means to keep the data center working. Typically in data centers, counterpart elements exist. When an access router fails for example the counterpart handles the load. However, this leads to elements use only 50% of greatest capacity. Multiple paths are not successfully used in current data center network capacity. A vast majority of data centers use TCP (Transmission Control Protocol) for communication. This communication usually takes place among the nodes and Incast. This occurs in many to single environment, which is dissimilar from the usual assumptions TCP based its design. In simple and more understandable words, TCP is unsuitable for a special data center environment with low latencies and high bandwidths thus limiting the optimum use of all capacity. In casting a receiver, requests data from multiple senders. Upon receiving the demand, the senders start sending out data to the original receiver simultaneously with the other senders. Nevertheless, in the middle of the connection from sender to receiver, is a bottleneck link resulting in a fall down in the receiver receiving the data. The result is network jamming from using the same bottleneck link. Advancing and increasing the buffer sizes of switches and routers hinders congestion, but in high latency and bandwidth data center environment, the buffers can still fill up in a short phase. In addition, large buffer switches and routers are costly.

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Power Distribution Architecture of a Data Center

A traditional power distribution architecture which was developed in the late 70’s is still being used by some of the existing data centers. In this basic system, the main power of the data center is distributed through ‘power distribution units (PDU, with 50kW- 500kW ratings)’. These units have large power transformers which provide voltage conditioning or voltage conversion. The power distribution units are in turn distributed to a quantity of branch circuits (with 1.5kW to 15kW ratings) to the IT equipment, where each IT enclosure uses one or more branches. The wiring to the IT enclosures is usually located beneath the raised floor.

However, when the traditional power distribution system was created, the data centers consisted of a small number of large IT devices which were hardly changed except during the scheduled stoppage of a major IT upgrade. The data centers in the present day have different characteristics that have challenged the traditional architecture, like:
• Constant addition of new power circuits due to the varying power requirements, without disturbing the nearby existing loads.
• With increase in per-rack power density, requirement for multiple branch circuits per cabinet is increased.
• There is no mechanism yet to monitor the circuit overloading above 50% in the commonly implemented dual power path systems.
• Data centers may contain thousands of plug-in devices with separate power cords, instead of a few large IT devices which require several more power receptacles.
• It is very difficult to determine impending overload conditions and to size branch circuits, when a large number of IT devices are connected to a branch circuit breaker

The characteristics of an ideal power distribution system would be:
• No under-floor cables
• Maintenance of capacity and redundancy on every circuit
• Addition or alteration of new circuits can be performed safely on a live system
• All circuits are monitored for power
• Should be able to deploy IT zones and associated power distribution over time
• Excess copper is not installed which is not necessary
• High Efficiency

In accordance with the varying needs of the modern data center, the power distribution systems have been evolving, and over time, various improvements have been introduced to these systems, a few notable ones being:
• Flexible power cords and overhead cable tray
• Less power distribution units of transformers
• Branch circuit metering for power
• High power and pluggable rack power distribution units
• Software for power capacity management

In order to suit a high density data center, the power distribution system should include all the above mentioned elements in its architecture.

The power distribution system has two steps: For larger data centers the main critical bus power from the uninterruptible power supply (UPS) is distributed to IT rows using one or more overhead busways. The busways are installed initially which traverse the entire IT rack layout. When a group of racks is to be installed, a low-footprint modular PDU is installed at the same time and plugged

In place of the traditional circuit breaker panels possessing raw wire terminations, we have the modular PDU that contains a backplane into which pre-terminated shock-safe circuit breaker modules are installed. This varied arrangement results in elimination of on-site termination of wires, and also allows the face of the PDU to be much narrower.

There are no initial branch circuits installed in the modular PDU. The power connection from the PDU to the IT racks comprise of flexible cable which can be plugged into the front of the modular PDU onsite depending on requirement of each specific rack. The branch circuit cables to the IT enclosures are pre-terminated with breaker modules that plug into the shock-safe backplane of the modular PDU.

A few particular equipments like blade servers which require a dedicated branch circuit generally possess a single cable from the PDU carrying either one, two or three branch circuits which directly plugs into the blade server, without any additional rack PDU needed. In case of presence of mixed equipment in the rack, we have the rack PDUs which can provide receptacle and current ratings which are interchangeable.

We encounter situations where we have racks of very high density, or a small group of racks being isolated by shape of the room or other constraints, wherein one or more zones within the data center might require only a small number of branch circuits. In these cases, the full 24-branch circuit capability of the standard modular distribution system is not needed. To overcome this, the architecture includes a smaller version of the modular power distribution unit, which supports up to 6 branch circuits and consumes zero floor footprint are directly mounted into an IT rack. The status and energy monitoring capability of the larger floor unit in a 5U rack mount version is included in the PDU.

The circuits can be further simplified for smaller data centers of 200kW or below, where the modular PDU may be integrated directly with the UPS system into a compact arrangement that can be located in the IT room. The requirement for a main bus wiring and separate power room is eliminated in such a setup.

Constant monitoring of current and energy on every circuit in a power distribution system is required at all levels of hierarchy. Simple network management protocols (SNMP) are used for monitoring the system. Also there is Capacity management software which monitors every circuit in the system and enforces safety margins, identify available capacity and verify redundancy.

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