JFS Tuning and Performance

The kernel tunable vxfs_bc_bufhwm specifies the maximum amount of memory in kilobytes (or high

water mark) to allow for the buffer pages. By default, vxfs_bc_bufhwm is set to zero, which means the

default maximum sized is based on the physical memory size (see Table 5).

The vxfsstat(1M) command with the -b option can be used to verify the size of the VxFS metadata

buffer cache. For example:

# vxfsstat -b /

: :

buffer cache statistics

120320 Kbyte current 544768 maximum

98674531 lookups 99.96% hit rate

3576 sec recycle age [not limited by maximum]

Note

The VxFS metadata buffer cache is memory allocated in addition to the HP-

UX Buffer Cache or Unified File Cache.

VxFS inode cache

vx_ninode

VxFS maintains a cache of the most recently accessed inodes in memory. The VxFS inode cache is

separate from the HFS inode cache. The VxFS inode cache is dynamically sized. The cache grows as

new inodes are accessed and contracts when old inodes are not referenced. At least one inode entry

must exist in the JFS inode cache for each file that is opened at a given time.

While the inode cache is dynamically sized, there is a maximum size for the VxFS inode cache. The

default maximum size is based on the amount of memory present. For example, a system with 2 to 8

GB of memory will have maximum of 128,000 inodes. The maximum number of inodes can be tuned

using the system wide tunable vx_ninode. Most systems do not need such a large VxFS inode cache

and a value of 128000 is recommended.

Note also that the HFS inode cache tunable ninode has no affect on the size of the VxFS inode cache.

If /stand is the only HFS file system in use, ninode can be tuned lower (400, for example).

The vxfsstat(1M) command with the -i option can be used to verify the size of the VxFS inode cache:

# vxfsstat -i /

: :

inode cache statistics

58727 inodes current 128007 peak 128000 maximum

9726503 lookups 86.68% hit rate

6066203 inodes alloced 5938196 freed

927 sec recycle age

1800 sec free age

While there are 128007 inodes currently in the VxFS inode cache, not all of the inodes are actually

in use. The vxfsstat(1M) command with the -v option can be used to verify the number of inodes in

use:

# vxfsstat -v / | grep inuse

vxi_icache_inuseino 1165 vxi_icache_maxino 128000