HP Integrity NonStop J-Series - Manual (Page 56)

Configuring and Managing SMF Processes
HP NonStop Storage Management Foundation User's Guide—523562-007
3-6
Considerations for Data
Virtual Disk Process Cache
The Virtual Disk Process cache can improve the performance of file OPENs and other
operations that access files by name by avoiding a catalog look up. The effectiveness
of VDP cache depends on its size and pattern of access. The cache must be large
enough so that the name of a file stays in cache between the time it is created and
opened; otherwise, the cache entry will be overlaid. If files are opened immediately
after they are created, a small VDP cache is sufficient; otherwise, a large cache will be
needed. The Enscribe file system has a simple one-entry cache, which may be
adequate in some cases. See
VDP and File System Caches on page 2-4 for more
details about the VDP and Enscribe caches.
VDP cache entries are 90 bytes each and are kept in memory. A very large cache can
increase memory pressure. For this reason, the default VDP cache size is zero. You
should set the VDP cache at a level that is large enough to improve performance but
not so large as to cause memory problems, which can impact performance. Increasing
cache size can be done after the application is up and running. For example, if
application start up time is a problem, identify the VDPs where the most files are
created, and increase their cache sizes to improve performance.
Considerations for Data
When planning an SMF configuration, consider:

The data files that must be located on SMF virtual disks

The files that must be left directly accessible on physical disks
Some types of data cannot be placed on virtual disks due to restrictions within SMF.
Other types of data should be left directly accessible for performance or operational
reasons. In some cases, leaving data directly accessible can reduce the overall size
and resource requirements of the SMF configuration.
The total number of virtual disks needed to manage a large amount of data depends
on the size of the drives used inside a storage pool. The G06 and later product
versions of SMF support the creation of format 2 files. Under SMF, each partition
requires a virtual disk process. Therefore, the size of each partition depends on the
free space available on the drive in a storage pool on which the virtual disk is
configured.
Data that must be left directly accessible due to SMF restrictions includes:

$SYSTEM files

Swap files

TMF audit trail files

DSM/SCM files

OSS file systems