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Optimizing Disk Performance

In any system, a balance must always be struck between cost, performance, and risk. If speed is the main concern, RAID 0 becomes an option, but the data on the RAID will be in serious jeopardy of being lost. The best overall strategy to optimize performance is to separate drives and devices based on speed and function.

Windows NT functions to a large extent via thread and thread handling. Each thread is assigned a priority; a thread with a higher priority can interrupt a thread with a lower priority. In fact, a client thread that spawns a server thread is preempted by that server thread. This was why video and printer drivers were moved to ring 0 in NT Version 4.0 - to avoid unnecessary thread disruption. To optimize NT performance, the trick then is to provide separate paths for disruptive threads (threads that interrupt normal processing).

So what steps should be taken? First, place the operating system and its page file on a controller or channel by itself. Place any NT utilities and related applications on this drive. Only include applications that are not speed-sensitive.

Second, place all data and applications on a separate drive on a different controller or controller channel. For example, a convenient entry-level server would have a 2GB boot drive on channel A of an Adaptec 3940uw and all applications on a larger (maybe 4GB) on channel B. Because this card allows multiplexing, both channels can be active at nearly the same time. In this manner, activating the page file on channel A will not be very preemptive (destructive) to tasks on B.

Finally, place all slow devices on a separate controller. For this configuration, you can use a 3940u and put tape drives, scanners, and CD-ROMS on one channel, and devices such as a CD-R on the other channel. Setting up systems with hardware as described here can dramatically improve NT performance.

Source: Windows NT Backup & Recovery, Osborne, 1998

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