Common Misconfigured HP-UX Resources (April 2006)

The JFS Inode Cache is a Dynamic Cache
Unlike the High Performance File System (HFS), the JFS inode cache is a dynamic cache. A dynamic
cache is a cache that grows and shrinks based on need. As files are opened, the number of inodes in
the JFS inode cache grows. As files are closed, they are moved to a free list and can be reused at a
later time. However, if the inode is inactive for a certain period of time, the inode is freed and space
is return to the kernel memory allocator. Over time, the numbers of inodes in the inode cache will
grow and shrink.
Maximum Inodes in the JFS Inode Cache
While the JFS inode cache is dynamically sized, there is still an absolute maximum number of inodes
that can be maintained in the inode cache. The following table shows the default maximum number of
inodes in the JFS inode cache
1
:
Physical Memory Default Maximum Inodes
for JFS 3.3 and above
256 Mb 16,000
512 Mb 32,000
1 GB 64,000
2 GB 128,000
8 GB 256,000
32 GB 512,000
128 GB 1,024,000
Specific values exist for memory sizes less than 256 Mb, but the sizes are not mentioned here since
most HP-UX systems should be using 256 Mb of memory or more. For systems equipped with
memory cells that can be configured as removable, memory in the above table refers to kernel
available memory and does not include removable memory.
If the size of memory falls in between the memory sizes listed in the previous table, a value
proportional to the two surrounding values is used. For example, a system using JFS 3.3 with 5 GB of
memory would have a default maximum number of inodes in the inode cache of 192,000.
Note the default maximum number of inodes seems very high. Remember that it is a maximum, and
the JFS inode cache is dynamic, as it can shrink and grow as inodes are opened and closed. The
maximum size must be large enough to handle the maximum number of concurrently opened files at
any given time, or the “vx_iget - inode table overflow” error will occur.
For JFS 3.3, you can identify the maximum number of JFS inodes that can be in the JFS inode cache
using the following adb command:
# echo “vxfs_ninode/D” | adb –k /stand/vmunix /dev/mem
1. JFS 3.3 is supported on 11i v1; JFS 3.5 is supported on HP-UX 11i v1 and 11i v2; and JFS 4.1 is supported
on HP-UX 11i v2, HP-UX 11i v3; and JFS 5.0 is supported on HP-UX 11i v2, HP-UX 11i v3 (planned).
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