Performance Tuning for the Storage Subsystem




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Choosing Server Hardware: Power Considerations


Although this guide focuses primarily on how to obtain the best performance from Windows Server 2008 R2, you must also recognize the increasing importance of energy efficiency in enterprise and data center environments. High performance and low energy usage are often conflicting goals, but by carefully selecting server components you can achieve the correct balance between them.

Table 3 contains guidelines for power characteristics and capabilities of server hardware components.



Table 3. Server Hardware Energy Saving Recommendations

Component

Recommendation

Processors

Frequency, operating voltage, cache size, and process technology all affect the energy consumption of processors. Processors have a thermal design point (TDP) rating that gives a basic indication of energy consumption relative to other models. In general, opt for the lowest-TDP processor that will meet your performance goals. Also, newer generations of processors are generally more energy efficient and may expose more power states for the Windows power management algorithms, which enables better power management at all levels of performance.

Memory (RAM)

Memory accounts for an increasing fraction of total system power. Many factors affect the energy consumption of a memory DIMM, such as memory technology, error correction code (ECC), bus frequency, capacity, density, and number of ranks. Therefore, it is best to compare expected power ratings before purchasing large quantities of memory. Low-power memory is now available, but you must consider the performance and cost trade-offs. If your server will be paging, then you should also factor in the energy cost of the paging disks.

Disks

Higher RPM means increased energy consumption. Also, new 2.5-inch drives require less than half the power of older 3.5-inch drives. For more information about the energy cost for different RAID configurations, see “Performance Tuning for Storage Subsystem” later in this guide.

Network and storage adapters

Some adapters decrease energy consumption during idle periods. This is an important consideration for 10-Gb networking adapters and high-bandwidth (4-8-Gb) storage links. Such devices can consume significant amounts of energy.

Power supplies

Increasing power supply efficiency is a great way to reduce energy consumption without affecting performance. High-efficiency power supplies can save many kilowatt-hours per year, per server.

Fans

Fans, like power supplies, are an area where you can reduce energy consumption without affecting system performance. Variable-speed fans can reduce RPM as system load decreases, eliminating otherwise unnecessary energy consumption.

USB devices

Windows Server 2008 R2 enables selective suspend for USB devices by default. However, a poorly written device driver can still disrupt system energy efficiency by a sizeable margin. To avoid potential issues, disconnect USB devices, disable them in the BIOS, or choose servers that do not require USB devices.

Remotely managed power strips

Power strips are not an integral part of server hardware, but they can make a large difference in the data center. Measurements show that volume servers that are plugged in but have been ostensibly powered off may still require up to 30 watts of power. To avoid wasting electricity, you can deploy a remotely managed power strip for each rack of servers to programmatically disconnect power from specific servers.





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Performance Tuning for the Storage Subsystem

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