Common Misconfigured HP-UX Resources (April 2006)

However, the memory cost must be considered. If the system is already running close to the low
memory threshold, the increased memory usage can consume memory that could potentially be used
for other applications, potentially degrading the performance of other applications.
Note that file systems with a large number of small files can have much more metadata than a larger
file system with a smaller amount of large files. There is no way to predict how much metadata will be
brought into the cache.
Consider the following example, a 2-GB system with dbc_max_pct parameter set to 20 percent
running JFS 3.3 on 11i v1:
The JFS file system is then upgraded to JFS 3.5. The dbc_max_pct parameter is still 20 percent, but
the metadata buffer cache has an additional 12 percent of memory. If the metadata cache is fully
used, then less space exists for other applications. If you still desire to use only 20 percent for the
buffer cache for both data and metadata, then the tunables must be evaluated and changed.
As a suggestion, consider the maximum amount of data and metadata that is desired, and then
consider the amount of metadata as a percentage of overall data. Going back to the previous
example, if the system should use a maximum of 20 percent of memory for both data and metadata,
and you desire a 90/10 ratio of data to metadata, then change dbc_max_pct to 18 and
vx_bc_bufhwm to 40,000 (or 40 Mb which is 2 percent of the 2 GB physical memory).
Note that this example uses a 90/10 ratio of data to metadata. The ratio you choose may be
different depending on your application usage. The 90/10 ratio is probably good for applications
that use large files, such as database applications. Applications that use lots of small files with
frequent file creations/deletions or large directories, such as file servers, may need more space for
metadata, so a 60/40 or 50/50 ratio may be appropriate.
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