Power Management in Servers


Reducing power consumption in data centers is one of the major challenges faced by enterprises right now. We take a look at someof the upcoming technologies which aim to combat this problem.

Lately one of the major challenges enterprises are facing is to bring down cost of power consumption and cooling in their data centers. Even determining how much power a particular server in a data center is consuming is very difficult. In a typical scenario, a fixed amount of power is supplied to the room and from there onto the racks. The challenge here is to determine how many servers can be placed in a single rack without exceeding the limit. To achieve this, Data center managers typically go by the power consumption value present on the server. However, servers usually consume lesser power than what is written on their nameplate, and this scenario also leaves racks under utilized. Solution to this is simple. Data center managers require more visibility in to how much power is being consumed by the servers. They need to constantly monitor power consumption to better understand this server/rack utilization and perform power budgeting.

In a server, power management can be divided in various ways. One common way to divide this is at processor level, Chipset level, Operating System level and application level. To solve the aforesaid issues, there is a lot of development going on in reducing power consumption of servers at each level, and dynamic power management of servers. Vendors are looking for ways to lower the power consumption of servers according to the workloads being processed by them and dynamically reallocate power to servers when their workloads need more processing power. Here we will be looking at various new technologies related to power management of servers that have hit or are about to hit the market, which aim to improve upon power consumption considerably.

Power management in Intel’s Nehalem platform
Nehalem has an integrated micro-controller called Power control Unit or PCU. It has its own embedded firmware and dynamic sensors to monitor current, temperature and power in real time. Nehalem also has an integrated power gate which eliminates the problem of power leakage. Power enables per core C6 state i.e. every individual core can switch to near zero power state. This process is invisible to the OS, software as well as other cores. This functionality is further extended with Nehalem’s turbo mode feature in which when idle cores are shut, power is channeled to active cores in order to boost their performance.

Source: Intel Nehalem has an integral power control unit with its own embedded firmware and dynamic sensors to monitor power in real time.Intel Dynamic Power Node Manager
This is an out-of-band power management policy engine which is embedded in Intel server chipset. It works along with the BIOS, OS and power management functions. It measures server’s actual power consumption with a margin of plus or minus 10% and generates reports. Users can track how much power is consumed by a server over a particular period of time. Let’s say a server consumes a maximum of 300 watts over a period of time and the budgeted power for the server is 600 watts, knowing this you can easily lower budgeted power to 400 watts. Node manager also supports power capping. It can enforce a policy set in server management console. It receives the policy through IPMI interface and maintains power by adjusting the CPU p-states.AMD Smart Fetch
Bit similar to Intel, AMD Shanghai has a technology called Smart Fetch, which can power down idle cores. As per AMD, this will reduce Power consumption of CPU by 21%. It also has AMD Cool core technology that reduces the power unused part of the processor, to reduce power consumption further. Next version of AMD server processor Istanbul might have a feature called Cool Speed. This processor provides protection to processor integrity by reducing the power states when it reaches a temperature limit. This will help platform providers in reducing system fan speeds which eventually could result in better efficiency.

Example of P-state being used to reduce power consumption in Windows Server 2008 R2.

Core parking
This is a new development in Windows server 2008 R2, which is currently available in its Beta. Core Parking constantly tracks workloads processed by every core, and consolidates the workload to a minimum possible cores and deactivates the inactive cores, thus saving on the un-necessary power being consumed by the inactive cores. Similarly when suddenly a workload requires more processing power, it activates the remaining cores. Along with this, Beta of Windows server 2008 R2 can reduce server power consumption by modifying ACPI ‘p-states’.

Also with this, power consumption of the server can be monitored through the system center and power budgeting can also be performed. Just to refresh your memory, P-States’ are performance states defined under ACPI specification. More details about ACPI can be found at www.acpi.info

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