HP NonStop G-Series - Manual (Page 37)

Preparing to Use SMF
HP NonStop Storage Management Foundation User's Guide—523562-008
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SMF Installation Considerations
If you perform a TMF initialization operation, SMF catalogs remain accessible, but SMF
catalog recovery protection is lost. In order to reestablish protection without dumping
enabled, you must perform TMF online dumps.
SMF Installation Considerations
Generally, SMF and location independent naming can be introduced without changes
to existing applications and most operational procedures.
The control flow path for operations such as file creation, open, purge, some file alters,
and informational requests has changed for SMF logically named files. Because the
NonStop S-series file systems use VDP services at various times to choose and
retrieve physical file locations, the new logical file access path has performance
implications, operational issues, and remote file access considerations. In addition,
there are application level considerations for those applications that treat the file
name’s volume component as the location for the file.
Performance Impact
Performance considerations derive from additional interprocess messages and
database lookups or updates that can be required for file creation, purge, access,
rename, and informational requests. The number of additional messages and database
accesses varies with the operation. There are no additional messages for file read and
write operations; therefore, performance of these operations is unchanged.
SMF is commonly used to map data from multiple small disks onto newer, larger disks.
The new configuration has fewer disk drives which can result in head contention, and
therefore increased latency if the disk reaches its peak I/O rate. You must analyze the
data to be consolidated and avoid placing many active files on the same disk.
Application Performance Considerations
In general, an application’s file access performance using virtual disks should be no
different than that of the same application accessing direct files. However, there are
additional messages and database accesses that extend the path length for file
creation, purge, and some open requests, in addition to various informational requests
(file-code alters and file rename operations). This extended path length applies only to
logically named Enscribe and SQL files, both temporary and permanent.
Open Operations
Open operations are considered performance critical. The file system might send an
additional message to the virtual disk process to obtain the logical-to-physical mapping
of the file, if it is not present in cache. However, in some cases, it may be possible for
the virtual disk process to obtain the physical location of the file without reading from its
own database. For more information, see
VDP and File System Caches .