Performance Tuning Guidelines for Windows Server 2008 May 20, 2009

Performance Tuning for Server Hardware

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

Table 1. Server Hardware Recommendations

Component	Recommendation
Processors	When the option is available, choose 64-bit processors because of the benefit of additional address space. Research data shows that two CPUs are not as fast as one CPU that is twice as fast. Because it is not always possible to obtain a CPU that is twice as fast, doubling the number of CPUs is preferred, but does not guarantee twice the performance. It is important to match and scale the memory and I/O subsystem with the CPU power and vice versa. Do not compare CPU frequencies across manufacturers and generations because the comparison can be a misleading indicator of speed.
Cache	Choose large L2 or L3 processor caches. The larger caches generally provide better performance and 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 needs more immediately, modern operating systems use hard disk space to supplement system RAM through a procedure called paging. Too much paging degrades overall system performance. You can optimize paging by using the following guidelines for pagefile placement: Place the pagefile and operating system files on separate physical disk drives. Place the pagefile on a drive that is not fault-tolerant. Note that, if the disk dies, a system crash is highly possible. If you place the pagefile on a fault-tolerant drive, remember that some fault-tolerant systems experience slow data writes because they write data to multiple locations. Use multiple disks or a disk array if additional disk bandwidth is needed for paging. Do not place multiple pagefiles on different partitions of the same physical disk drive.
Peripheral Bus	To avoid bus speed limitations, use either PCI-X or PCIe x8 and higher slots for Gigabit Ethernet adapters.
Disks	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. The latest generation of 2.5-inch enterprise-class disks can service a significantly larger number of random requests per second compared to 3.5-inch drives. Store “hot” data near the “beginning” of a disk because this corresponds to the outermost (fastest) tracks. Avoid consolidating small drives into fewer high-capacity drives, which can easily 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 recommends characteristics for network and storage adapters for high-performance servers. These characteristics can help keep your networking or storage hardware from being the bottleneck when they are under heavy load.

Table 2. Networking and Storage Adapter Recommendations

Recommen-dation	Description
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 limited 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 more attached disks are possible 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 PCI slot that provides enough bandwidth. Generally, PCI‑E adapters provide more bandwidth than PCI‑X adapters.
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.
Offload capability and other advanced features such as message-signaled interrupt (MSI)-X	Offload-capable adapters offer CPU savings that translate into improved performance. For more information, see “Choosing a Network Adapter” later in this guide.
Dynamic interrupt and deferred procedure call (DPC) redirection	Windows Server 2008 has new functionality that enables PCI-E 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. At Windows Server 2008 RTM, no adapters on the market had this capability, but several manufacturers were developing adapters to take advantage of this performance feature.