HP Integrity NonStop J-Series - Manual (Page 40)

Preparing to Use SMF
HP NonStop Storage Management Foundation User's Guide—523562-007
2-6
Performance Impact
different physical devices can experience unexpected results in performance,
availability, or space distribution.
Similarly, two files with the same volume component might be on different physical
devices. This can occur since a VDP may place files on any physical volume in the
storage pool, subject to availability, space, and other criteria. Therefore, applications
designed to operate as if the availability and performance of two files are the same
because the volume components of their file names match can also experience
unexpected results.
Application developers and operational users can make use of the PHYSVOL option of
the FILE_CREATELIST_ file system procedure, and the TACL, FUP, or SQLCI
CREATE and RESTORE commands to ensure that the VDP creates the file on the
appropriate physical volume. The FUP RELOCATE command can also be used to
move files that already exist.
File Information by Name
There are various file information requests that retrieve information by name. These
requests can show a performance degradation when done for logically named files.
FILE_GETINFO[LIST]BYNAME_FILEINFO, NEXTFILENAME
These types of requests obtain information about a single file. They are available to
applications and are also called by higher level functions such as TACL, FUP, and SQL
FILEINFO. These file system procedures retrieve various pieces of information about
the file from the file label and from the VDP catalog.
Where possible, the name caches described previously (see VDP and File System
Caches on page 2-4) are used to reduce the search time.
The NEXTFILENAME interface (and related privileged interfaces) can be used to
iterate through files on the disk, resulting in a VDP catalog read for each name
returned. Note that the name caches are not used for these requests.
Any critical processes and operational procedures bound by the performance of file
information requests may see a performance degradation. Applications that include
such processes or procedures would benefit from redesign or from using direct files.
Such degradation could affect TACL users who use wild cards: for example, FILEINFO
$L.*.*.
FILENAME_FIND*_
Applications use this calling sequence to iterate through file names for pattern
matching. The information needed to satisfy this request comes only from the VDP
catalog; that is, DP2 is not involved. Therefore, any performance degradation comes
only from the VDP catalog reads. FILENAME_FIND* performance on a virtual disk is
comparable to the performance of the same command on a direct volume where few
directory blocks are cached.