Optimizing File System Performance

In Windows 98, the disk cache is dynamic. You do not need to configure its size as part of system configuration. Because of this, certain settings used for Windows 3.x are not required in Windows 98 and should be removed from the configuration files. Table 26.2 shows these settings.

Table 26.2 Configuration settings not required

The overall performance, for example, of a computer with 16 MB of memory is better under Windows 98 than under Windows 3.1. However, the amount of paging might increase under Windows 98 for the following reasons:

• Windows 98 aggressively writes the contents of dirty memory pages (pages that contain changes) during system idle time, even if it does not need the memory then. This causes more idle-time disk activity but speeds up future memory allocations by doing some of the work while the system is idle.
• Much more of Windows 98 can be paged out to disk than Windows 3.1.

Changing the cache size is not a good method of limiting paging. Paging through the cache would quickly overwhelm it and make it useless for other file I/O. Although swap file I/O operations do not go through the cache, memory-mapped files and executable files do. The cache, however, is designed to make sure it cannot be overwhelmed by such I/O operations.

Changing the cache size (even if you could) probably would not have much effect on paging. The cache grows and shrinks as needed. If the system begins to page a lot, the cache shrinks automatically. However, people often think they are seeing a lot of paging, but they are really seeing other disk activity, such as Windows 98 building its icon cache or the cache lazy writing.

A common reason for excessive paging is that the working set of the applications you are running is greater than the amount of physical RAM available. If the amount of paging is extreme, to the point where system performance is poor, a real-mode driver for the hard disk may be the cause, and should be replaced with a protected mode driver. If Windows 98 needs to use real-mode for its disk I/O operations, a lot of code has to be locked down that would otherwise be pageable, and your working set increases significantly.

Note

Paging through a real-mode driver increases paging, and on a computer with 16 MB of memory (the minimum configuration for Windows 98), it can cause unacceptable performance.

Optimizing File System Performance with Profiles

In Windows 98, file system and disk performance can be controlled based on how the computer is used in most situations. The option for configuring file system performance is controlled only by the user. None of these settings are affected by other configuration changes that might be made in Windows 98, such as installing file and printer sharing services, or choosing the Portable option as the setup type when installing Windows 98.

Note

Application launch acceleration depends on cluster size and, therefore, the particular file system. Smaller cluster sizes give better application launch performance—the 4 KB cluster size (FAT32) is best; larger sizes (for example, FAT16) give less of a performance boost.

To optimize file system performance

1. In Control Panel, double-click System, click the Performance tab, and then click File System.
2. In the Typical role of this computer box, select the most common role for this computer, and then click OK. Table 26.3 describes each role in the list.

Table 26.3 Computer role descriptions

Each disk performance profile adjusts the values of the following file system settings in the registry:

• PathCache specifies the size of the cache that the virtual file allocation table (VFAT) can use to save the locations of the most recently accessed directory paths. This cache improves performance by reducing the number of times the file system must seek paths by searching the file allocation table. The number of paths is 32 for the Desktop computer profile, 16 for Mobile or docking system, and 64 for Network server.
• NameCache stores the locations of the most recently accessed file names. The combined use of PathCache and NameCache means that VFAT never searches the disk for the location of cached file names. Both PathCache and NameCache use memory out of the general system heap. The number of file names is about 677 (8 KB) for the Desktop computer profile, 337 (4 KB) for Mobile or docking system, and 2729 (16 KB) for Network server.
• BufferIdleTimeout, BufferAgeTimeout, and VolumeIdleTimeout control the time between when changes are placed in the buffer to when they are written to the hard disk.

The values to be assigned to each disk performance profile are stored in the following registry key:

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\FS Templates

The following subkey contains the actual settings for the profile currently used:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\FileSystem

An additional performance setting in the FileSystem subkey, ContigFile AllocSize, can be used to change the size of the contiguous space that VFAT searches for when allocating disk space. Under MS-DOS, the file system began allocating the first available space found on the disk, which ensured a great deal of disk fragmentation and related performance problems. By default under Windows 98, VFAT first tries to allocate space in the first contiguous 0.5 MB of free space and then returns to the MS-DOS method if it cannot find at least this much contiguous free space. This optimizes performance for both the swap file and multimedia applications.

In some cases, you might choose to set a smaller value in the registry, as when you are not running demanding applications on the computer. A smaller value for ContigFileAllocSize, however, can lead to more fragmentation on the disk and, consequently, more disk access for the swap file or applications that require larger amounts of disk space.

Optimizing CD-ROM File System Performance

The CD-ROM cache is separate from the cache used for disk file and network access because the performance characteristics of the CD-ROM are different. This cache can be paged to disk (the file and network cache cannot), reducing the working set for Windows 98 but still allowing for better CD-ROM performance. When Windows 98 is retrieving data from a compact disc, it is still faster to read a record from the cache even if it has been paged to disk, because the disk-access time is much faster than the compact disc–access time.

Tip

A small CD-ROM cache makes a big difference in streaming performance, but a much larger cache does not pay off as significantly, unless the cache is large enough to contain entire multimedia streams.

To set the supplemental cache size for CDFS

1. In Control Panel, double-click System, click the Performance tab, and then click File System.
2. Click the CD-ROM tab, and drag the slider to set the Supplemental cache size.

   Move the Supplemental Cache Size slider to the right to allocate more RAM for caching data from the CD-ROM drive or to the left to allocate less RAM for caching data.

   Note

   Many multimedia programs perform better with a smaller cache, because they tend not to reuse data.

3. In the Optimize access pattern for box, select a setting based on your computer’s CD-ROM drive speed. Table 26.4 shows the size of the cache created for each CD-ROM drive speed setting.

   Table 26.4 Optimizing cache size

4. Click OK, and then shut down and restart the computer.

Optimizing DVD File System Performance

Digital video discs (DVDs) primarily use the Universal Disk Format (UDF) for their file systems. UDF uses the main file system cache (VCACHE), and there are no performance settings for end users to change.

For more information about UDF, see Chapter 10, "Disks and File Systems."

For more information about DVD, see Chapter 10, "Disks and File Systems," and Chapter 30, "Hardware Management."

Optimizing Removable Disk Drive Performance

Windows 98 gives you the option to use write-behind caching to improve the performance of removable disk drives, such as the ZIP or JAZ drive.

To set write-behind caching for removable disk drives

1. In Control Panel, double-click System, click the Performance tab, click File System, and then click the Removable Disk tab.
2. Select the Enable write-behind caching on all removable disk drives check box. Click OK.
3. If this causes a problem with disk operations, follow step 1, and then click to clear the Enable write-behind caching on all removable disk drives check box. Click OK.

Optimizing I/O Transfers by Using Direct Memory Access

The advantage of using direct memory access (DMA) with integrated device electronics (IDE) CD-ROM and disk drives is that it allows much lower CPU usage during I/O transfers for drives that are part of an original equipment manufacturer (OEM) computer. DMA is enabled by default in OEM computers, but because certain older IDE drives can corrupt data when using DMA, care must be taken when enabling DMA in upgraded computers.

To enable DMA

1. In Control Panel, double-click System, and then click the Device Manager tab.
2. Select an IDE device under the CD-ROM branch or the Disk drives branch, and click Properties.
3. Click the Settings tab, and then check off the DMA check box.
4. Click OK, and then shut down and restart the computer.

Using File System Troubleshooting Options

The System option in Control Panel presents a set of options for changing file system performance. You can use these options when you experience rare hardware or software compatibility problems.

Important

Enabling any of the file system troubleshooting options will seriously degrade system performance. Typically, you want to enable these options only if instructed to do so by a product support representative. Otherwise, these options should rarely, if ever, be used.

To display the file system troubleshooting options

1. In Control Panel, double-click System, and then click the Performance tab.
2. Click File System, and then click the Troubleshooting tab.

Table 26.5 summarizes the settings in Troubleshooting properties. Each option sets a value in the following registry key.

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\FileSystem

Table 26.5 File system troubleshooting options