Six steps to improving disk throughput

Typically, in Windows 2000 the common symptoms of storage system problems are persistent disk queues longer

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than two per disk, sustained disk activity significantly higher than your baseline number and a lack of a significant amount of paging. While the disk system is the logical suspect in performance degradation, it's not the only possible culprit. In a virtual memory operating system like Windows 2000, it may mean you need more memory.

If you are running short of RAM for the virtual memory, it will degrade storage system performance as the virtual memory constantly swaps pages in and out in an effort to meet the system's demands. In this case the cure is increasing the size of the paging file or adding more physical memory.

Because of the possibility of a memory problem, it is important to check the memory activity counters in System Monitor as well as the disk activity counters. Microsoft recommends checking memory pages/sec, memory page reads/sec and memory page writes/sec along with the disk activity counters.

Another possibility is that the disk hardware is issuing too many interrupts. Technically the source of the bottleneck in this case is the processor rather than the storage system, but the root cause is still in the storage system. Wherever possible, use intelligent drivers that minimize the number of processor interrupts.

If you do have a disk bottleneck though, there are a number of things you can do to relieve the strain. Here are five:

1. Try to find the hot spots in the system and as much as possible separate them. For example if you have two disks with I/O intensive workloads, try to put them on separate I/O busses.

2. Use striped volumes to spread the load of a read or write over multiple disks. If you match the size of the stripe to the size of the average request in your workload you will improve performance further.

3. If adding disks to a striped volume doesn't improve throughput, consider the possibility that the disks are contending for access to the disk adapter. Adding another adapter will spread the load and should improve performance.

4. In the case of an application like a database which reads and writes to separate files as part of an operation, try to put the various parts of the operation on separate disks. This can be especially significant in the case of applications which maintain transaction logs. Not only does an update to such and application require accessing separate files, but the characteristics of the files are very different. Transaction logs are usually sequential where the actual database is usually accessed at random.

5. Don't use file encryption or compression unless you really need them. Both compression and encryption can add enough overhead to make a difference in a bottlenecked system.

6. Defrag your disks regularly. Although disk fragmentation in Windows 2000 isn't the issue it was in earlier versions of Windows, defragmentation can still produce a considerable performance improvement.

For more information:

Tip: What causes slow startup in Windows 2000?

Tip: Nuances of Windows NT and SCSI disk performance

Tip: Simplify disk alignment in Windows 2000

Rick Cook has been writing about mass storage since the days when the term meant an 80K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last twenty years he has been a freelance writer specializing in storage and other computer issues..

This was first published in May 2004

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