HP NonStop G-Series - Manual (Page 38)

Preparing to Use SMF
HP NonStop Storage Management Foundation User's Guide—523562-008
2-4
Performance Impact
VDP and File System Caches
The following features have been designed to minimize the impact of SMF on open
performance:

VDP name cache. The VDP maintains a cache of file name mappings for both
permanent and temporary files. When a name mapping is requested, the VDP first
looks in its name cache. If the name mapping is present, it is used, avoiding the
need to access the VDP catalog. If the entry is not present in the cache, it is read
from the VDP catalog. When the entry is read from the VDP catalog, it is inserted
into the cache and the oldest entry is deleted if the cache is full. The VDP also
inserts a cache entry when an Enscribe file is created (Enscribe files only).

File system name cache. The file system stores the name mapping it most recently
obtained in the process file segment. If this is the name of the file to be opened,
the file system does not ask the VDP for the mapping. In this case, the difference
in open time between logically named files and direct files is negligible.
The file system name cache entry is stored when:

Information is requested on a logically named file (for example, by checking to
see if a file exists before opening it).

The file system does a resolve request as part of an open so that repeated
opens of the same file result in only one message to the VDP.

A file is created (Enscribe files only).
Swap Temporary Files
Extended segment and data stack SWAP files are generally created as temporary files.
They are created at process start time, which makes them performance critical.
Because there is a performance penalty associated with creating logical temporary
files, HP does not recommend that they be used for swap files where process creation
time is critical.
Program Files
There are no functional restrictions on placing program files on logical volumes.
However, doing so will increase process creation time. For applications where startup
time is critical, you should not place heavily used object files on logical volumes.
SQL Catalog Performance
The SQL Catalog Manager creates all SQL catalog files on the same disk if the user
specifies a PHYSVOL option during SQL catalog creation. Otherwise, the catalog files
are distributed among the physical disks in the SMF pool. See
SQL Catalog Availability
on page 2-12.