Open System Services Management and Operations Guide (G06.25+, H06.03+)

Managing Filesets
Open System Services Management and Operations Guide—527191-002
5-18
Changing OSS File Caching for the Disks of a
Fileset
OSS file caching enabled on one disk volume in a given fileset but disabled for another
disk volume in that fileset, you cannot predict whether a particular file might be cached.
If you want to add disks to a storage pool for a fileset that has OSS file caching
disabled:
1. Use the Subsystem Control Facility (SCF) storage subsystem to add the disks to
the system.
2. Modify the storage-pool file for the fileset.
3. Do one of the following:
a. Stop and start the fileset as described under Starting (Mounting) or Restarting
Filesets on page 5-6
b. Apply the change to the started fileset using the SCF CONTROL FILESET
Command with the SYNC option.
Caching Effects
The caching status of a file can change as opens, closes, and other events occur on
the file. The data integrity of a file and the access (data transfer) speed for the file are
affected by the following:
•
Whether OSS file caching is enabled
•
Which program access options are used, such as how the file is opened
•
What messages are exchanged through the NonStop operating system message
system
These effects are shown in Table 5-1.
Table 5-1. OSS File Caching, Data Integrity, and File Access Speed (page 1 of 2)
Caching Status
Data
Integrity Message Exchanges
Performance
(Access Speed)
Cached Lowest The number of messages
between the OSS file system
and the disk process is kept to a
minimum.
Highest performance
for serial access to
files
Not cached, file
does not have
S_NONSTOP
attribute set and
was not opened
with O_SYNC flag
Low Each input or output request
causes a message exchange
between the OSS file system
and the disk process.
Best performance
for random access
for programs that
perform read
operations larger
than 16 kilobytes