From the Hierarchical File System Usage Guide
Redbook at the following URL: http://www.redbooks.ibm.com/redbooks/pdfs/sg245482.pdf;
you will find a description of the virtual MAX BPX parmlib parameter.
"The VIRTUAL(max) parameter specifies the maximum amount of virtual
storage (in megabytes) that HFS data and metadata buffers should use.
The default is 50% of real storage available to the system at HFS
initialization time."
This parameter in practical experience is not often set by the customer.
The default being half of the physical memory at Unix System Services
start up is usually a large enough amount to not notice any performance
hits. Because of this lack of exposure and the processing of the VMAX
parameter being all within buffers in memory, problems are difficult and
time consuming to diagnose.
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