Veritas 4.1 Installation Guide (HP-UX 11i v3, February 2007)

A Appendix
The following topics are discussed here:
• “Controlling Memory Utilization of VxFS 4.1 on HP-UX 11i v3”
• “LVM Volume Groups to VxVM Conversion Error Messages”
Controlling Memory Utilization of VxFS 4.1 on HP-UX 11i v3
Introduction
VxFS 4.1 caches objects in memory to improve performance. Most of the memory consumed by
VxFS is used to cache inodes (in the inode cache) and metadata (in the buffer cache). The cache
size and VxFS behaviour is controlled by a set of tunables. The VxFS performance can be tuned
for a variety of usage scenarios based on system configuration using the various tunables. The
default settings of these tunables are meant to provide good performance for majority of
deployment scenarious. However, these default values can result in the VxFS driver consuming
more memory, especially when the file system is under heavy load. For machines with relatively
low total RAM, or relatively low in memory base cells (for systems equipped with memory cells
that can be configured as removable), these tunables may need to be manually tuned down
depending on the expected use of the machine and the performance required for the file system.
For more information, see “HP-UX 11i v3 Cell OL* Features and configuration recommendations”
whitepaper. VxFS 4.1 exposes two global tunables, vx_ninode and vxfs_bc_bufhwm, that
control the size of the inode cache and buffer cache, respectively, and thereby affect system
memory consumption by the file system driver.
This appendix discusses when and why the size of the inode and buffer caches need to be tuned
down from their default values in certain configurations. The following sections describe these
tunables in detail as well as the effects of changing their default values.
Controlling the inode Cache
VxFS file systems allocate and free up inodes as required by the load on the file system. VxFS
caches these inodes for better performance (faster lookups). In general, larger inode caches help
file systems perform better for file server and web server loads. The global (dynamic) tunable
vx_ninode represents the maximum possible size of the VxFS inode cache.
Normally, the size of the inode cache is decided (auto-tuned) at boot time by VxFS depending
on the amount of physical memory available on the system, provided that the value of vx_ninode
is set to zero (default).
VxFS defaults the inode cache size according to the following table:
Table A-1 VxFS Defaults Inode Cache Size
Default VxFS inode cache (number of inodes)Physical memory size in MB
640001024
1280002048
2560008192
51200032768
1024000131072
The first column represents physical memory in MB and the second column means the number
of inodes to be cached. VxFS interpolates for the memory that falls between two points. For larger
memory systems with greater than 128GB, VxFS extrapolates from the last entry.
However, for systems having low total RAM, or relatively low in memory base cells (having
typically up to 3 GB), the default setting for inode cache may allocate a lot of memory which can
be tuned down if and only if the file system performance is not critical for the intended usage
of the system. These systems may not require such a large inode cache if file systems are not
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