Common Misconfigured HP-UX Resources (April 2006)

The size of the cache is determined by the ninode tunable. Note that the tunable only sizes the HFS

inode cache, and does not affect the JFS inode cache. The tunable also sizes the HFS inode hash

table, which is the previous “power of 2” based on ninode. For example, if the ninode tunable is

configured for 1500 inodes, then the hash table will have 1024 hash entries (since 1024 is the

previous power of 2 to 1500).

When an inode lookup is performed, the device and inode number are both used to hash into the

inode hash table. From the hash header, a linked list of inodes that hash to the same hash header is

analyzed to see if the desired inode is found. If the desired inode is found, use the inode in memory.

If the desired inode for the file is not found, reuse the least recently used inode, which is the first inode

on the free list. The inode information on disk is then read into this newly obtained inode. If there are

no inodes on the free list, the system call will fail with the “inode table is full” message.

Determining the Memory Cost of the HFS Inode Cache

You can determine the cost of the HFS inode cache table by identifying the size of the inode hash

table and the actual cache of inodes. Note that the inode cache is simply an array of vnode/inode

structures (the vnode is the Virtual File System layer part). Since the vnode is actually part of the

inode, you only need to consider the size of the inode. You can use the following table to identify the

number of bytes needed per entry for each structure.

11i v1.5 11.0 32-bit 11.0 64-bit 11i v1 32-bit 11i v1 64-bit 11i v2

inode 336 336 488 367 496 576

hash entry 8 8 16 8 16 16

Using the previous table, you can calculate the memory cost of the HFS inode cache. For example, if

ninode is configured at 10,000 on an HP-UX 11i v1 64-bit system, then the system would use 4844

Kb for the HFS inode table ( 496*10000 / 1024), and 128 Kb for the HFS hash table (previous

power of 2 (8192) * 16 / 1024).

The HFS Inode Cache and the DNLC

The ninode tunable used to configure the HFS inode cache size can also impact the size of the

Directory Name Lookup Cache (DNLC). The size of the DNLC used to be entirely dependent on the

value of ninode. However, this caused some problems since the DNLC was used by HFS and non-

HFS file systems (such as JFS). For example, even if the /stand file system was the only HFS file

system, a customer would have to configure ninode very large in order to get a large enough DNLC

to handle the JFS files.