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Tuning NT Server Disk Subsystems: Tips for Keeping Your System in Tip-Top Shape

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This article by Windows NT/2000 tuning and sizing expert Curt Aubley focuses on tuning disk and disk subsystems (RAID).
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Performance! Everyone wants Windows NT servers and workstations to run as fast as possible. Keeping your disk subsystem running at its best is an important step in improving the overall performance of your NT solution. In my article "Sizing Your NT RAID Array," I show you how to determine when your NT disk subsystem becomes a bottleneck and how to size additional disk capacity for your NT system. But how do you get the most from an additional standalone hard disk or RAID array investment?

In this article, I'll show you how to maximize the performance of your extra disk capacity when implementing NT disk subsystems and RAID arrays, regardless of any vendor-specific hardware tweaks. You can use NT's built-in tools and a freeware tool to quickly optimize your disk subsystem (hardware- or software-based RAID). To accomplish this task, you must understand the performance characteristics of the standalone disk or RAID technology that you are working with and the workload characteristics of your existing disk subsystem. Using this information, you can load-balance your disk subsystem and tune the disk allocation unit size. Finally, because your performance increase can vary according to your computing environment, I'll show you how I tuned and tested my disk subsystem.

Common RAID Characteristics

Most systems administrators add disk subsystem capacity in the form of RAID arrays. When you use NT's internal software RAID technology or hardware-based vendor RAID technology, RAID 0, 1, and 5 are the most common RAID levels for NT Server environments. (For information about RAID level technology, see Table 1 in my article, Sizing your NT RAID Array.)

When you select RAID configurations, you need to consider many important factors, such as cost and availability level required, in addition to just performance; however, this article focuses on performance. For information about other factors to consider, see the third article in this series, "What to Look for When Selecting a Scalable RAID Array."

Regardless of the RAID level that you select, use a hardware-based RAID solution if you implement any NT solution that supports more than three disks and that requires any level of high availability and performance. Hardware-based RAID adapters and controllers provide much better performance than NT's built-in software-based solution provides and are particularly valuable when you implement RAID 5. With RAID 5, hardware-based RAID adapters offload parity processing and some of the associated interrupt traffic, unlike software-based RAID. This offloading results in improved overall NT performance.

When you're selecting the appropriate RAID level, consider the relative performance characteristics that each RAID level provides. Table 1 illustrates the relative performance level of the various RAID levels in several I/O workload environments and can help you match the appropriate performance to your system's disk I/O characteristics.

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