nbuf

Description

The nbuf parameter specifies the number of buffer headers in the file system buffer cache. The actual memory associated with each buffer header is dynamically allocated as needed and can be of varying size, currently 1 to 128 blocks (512 to 64KB).

The system uses the file system buffer cache to optimize file system I/O requests. The buffer memory caches blocks from the disk, and the blocks that are used frequently stay in the cache. This helps avoid excess disk activity.

Buffers are used only as transaction headers. When the input or output operation has finished, the buffer is detached from the memory it mapped and the buffer header becomes available for other uses. Because of this, a small number of buffer headers is sufficient for most systems. If nbuf is set to 0, the system automatically configures nbuf for average systems. There is little overhead in making it larger for non-average systems.

The nbuf parameter is defined in /var/sysgen/mtune.

Value

Default: 0 (Automatically configured if set to 0)

Formula: 100 + (total number of pages of memory/40)

32-bit Range: up to 6000

64-bit Range: up to 250000

When To Change

The automatic configuration is adequate for average systems. If you see dropping ''cache hit'' rates in sar and osview output, increase this parameter. Also, if you have directories with a great number of files (over 1000), you may wish to raise this parameter.