|
|
|
|
|
VxFS maintains its own buffer cache in the kernel for frequently accessed file system metadata. This cache is different from the HP-UX kernel buffer cache that caches file data. The vx_bc_bufhwm dynamic, global, tunable parameter lets you change the VxFS buffer cache high water mark, that is, the maximum amount of memory that can be used to cache VxFS metadata.
The initial value of vx_bc_bufhwm is zero. When the operating system reboots, VxFS sets the value of vx_bc_bufhwm based on the amount of system memory. You can explicitly reset the value of vx_bc_bufhwm by changing the value of vxfs_bc_bufhwm using the sam or kctune commands.
See the sam(1M) and kctune(1M) manual pages.
You can also set the value by adding an entry to the system configuration file. For example, the following entry:
vxfs_bc_bufhwm vx_bc_bufhwm 300000
sets the high water mark to 300 megabytes. The change takes effect after you rebuild the HP-UX kernel using the mk_kernel command. You specify the vx_bc_bufhwm tunable in units of kilobytes. The minimum value is 6144.
Increasing the value of vx_bc_bufhwm increases the VxFS buffer cache immediately, allowing a greater amount of memory to be used to cache VxFS metadata. Decreasing the value of vx_bc_bufhwm decreases the VxFS buffer cache to the specified value. This frees memory such that the amount of memory used for buffer cache is lower than the specified value of vx_bc_bufhwm.
Typically, the default value computed by VxFS based on the amount of system memory ensures good system performance across a wide range of applications. For application loads that cause frequent file system metadata changes on the system (for example, a high rate of file creation or deletion, or accessing large directories), changing the value of vx_bc_bufhwm may improve performance.
You can use the vxfsstat command to monitor buffer cache statistics and inode cache usage.
See the vxfsstat(1M) manual page.