Performance Tuning Guidelines for Windows Server 2012 April 12, 2013 Abstract

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Choosing Server Hardware: Performance Considerations

Table 1 lists important items that you should consider when you choose server hardware. Following these guidelines can help remove performance bottlenecks that might impede the server’s performance.

Table 1. Server Hardware Recommendations




Choose 64-bit processors for servers. 64-bit processors have significantly more address space, and are required for Windows Server 2012. No 32-bit editions of the operating system will be provided, but 32-bit applications will run on the 64-bit Windows Server 2012 operating system.

To increase the computing resources in a server, you can use a processor with higher-frequency cores, or you can increase the number of processor cores. If CPU is the limiting resource in the system, a core with 2x frequency typically provides a greater performance improvement than two cores with 1x frequency. Multiple cores are not expected to provide a perfect linear scaling, and the scaling factor can be even less if hyperthreading is enabled because hyperthreading relies on sharing resources of the same physical core.

It is important to match and scale the memory and I/O subsystem with the CPU performance and vice versa.

Do not compare CPU frequencies across manufacturers and generations of processors because the comparison can be a misleading indicator of speed.


Choose large L2 or L3 processor caches. The larger caches generally provide better performance, and they often play a bigger role than raw CPU frequency.

Memory (RAM) and paging storage

Increase the RAM to match your memory needs.

When your computer runs low on memory and it needs more immediately, modern operating systems use hard disk space to supplement system RAM through a procedure called paging. Too much paging degrades the overall system performance.

You can optimize paging by using the following guidelines for page file placement:

  • Isolate the page file on its own storage device(s), or at least make sure it doesn’t share the same storage devices as other frequently accessed files. For example, place the page file and operating system files on separate physical disk drives.

  • Place the page file on a drive that is not fault-tolerant. Note that, if the disk fails, a system crash is likely to occur. If you place the page file on a fault-tolerant drive, remember that fault-tolerant systems are often slower to write data because they write data to multiple locations.

  • Use multiple disks or a disk array if you need additional disk bandwidth for paging. Do not place multiple page files on different partitions of the same physical disk drive.

Peripheral bus

In Windows Server 2012, it is highly recommended that the primary storage and network interfaces are PCI Express (PCIe), and that servers with PCIe buses are chosen. Also, to avoid bus speed limitations, use PCIe x8 and higher slots for 10 Gigabit Ethernet adapters.


Choose disks with higher rotational speeds to reduce random request service times (~2 ms on average when you compare 7,200- and 15,000-RPM drives) and to increase sequential request bandwidth. However, there are cost, power, and other considerations associated with disks that have high rotational speeds.

2.5-inch enterprise-class disks can service a significantly larger number of random requests per second compared to equivalent 3.5-inch drives.

Store frequently accessed data (especially sequentially accessed data) near the “beginning” of a disk because this roughly corresponds to the outermost (fastest) tracks.

Be aware that consolidating small drives into fewer high-capacity drives can reduce overall storage performance. Fewer spindles mean reduced request service concurrency; and therefore, potentially lower throughput and longer response times (depending on the workload intensity).

Table 2 lists the recommended characteristics for network and storage adapters for high-performance servers. These settings can help prevent your networking or storage hardware from being a bottleneck when they are under heavy load.

Table 2. Networking and Storage Adapter Recommendations



WHQL certified

The adapter has passed the Windows® Hardware Quality Labs (WHQL) certification test suite.

64-bit capability

Adapters that are 64-bit-capable can perform direct memory access (DMA) operations to and from high physical memory locations (greater than 4 GB). If the driver does not support DMA greater than 4 GB, the system double-buffers the I/O to a physical address space of less than 4 GB.

Copper and fiber (glass) adapters

Copper adapters generally have the same performance as their fiber counterparts, and both copper and fiber are available on some Fibre Channel adapters. Certain environments are better suited to copper adapters, whereas other environments are better suited to fiber adapters.

Dual- or quad-port adapters

Multiport adapters are useful for servers that have a limited number of PCI slots.

To address SCSI limitations on the number of disks that can be connected to a SCSI bus, some adapters provide two or four SCSI buses on a single adapter card. Fibre Channel disks generally have no limits to the number of disks that are connected to an adapter unless they are hidden behind a SCSI interface.

Serial Attached SCSI (SAS) and Serial ATA (SATA) adapters also have a limited number of connections because of the serial nature of the protocols, but you can attach more disks by using switches.

Network adapters have this feature for load-balancing or failover scenarios. Using two single-port network adapters usually yields better performance than using a single dual-port network adapter for the same workload.

PCI bus limitation can be a major factor in limiting performance for multiport adapters. Therefore, it is important to consider placing them in a high-performing PCIe slot that provides enough bandwidth.

Interrupt moderation

Some adapters can moderate how frequently they interrupt the host processors to indicate activity or its completion. Moderating interrupts can often result in reduced CPU load on the host, but unless interrupt moderation is performed intelligently, the CPU savings might increase latency.

Receive Side Scaling (RSS) support

RSS is a technology that enables packet receive-processing to scale with the number of available computer processors. Particularly important with faster Ethernet (10 GB or more).

Offload capability and other advanced features such as message-signaled interrupt (MSI)-X

Offload-capable adapters offer CPU savings that yield improved performance. For more information, see Choosing a Network Adapter later in this guide.

Dynamic interrupt and deferred procedure call (DPC) redirection

Windows Server 2012 has functionality that enables PCIe storage adapters to dynamically redirect interrupts and DPCs. This capability, originally called “NUMA I/O,” can help any multiprocessor system by improving workload partitioning, cache hit rates, and on-board hardware interconnect usage for I/O-intensive workloads.

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Performance Tuning Guidelines for Windows Server 2012 April 12, 2013 Abstract

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