Open System Services Management and Operations Guide (G06.30+, H06.08+, J06.03+)

Table 10 Effects of File I/O Fault-Tolerance Attribute Settings (continued)
ResultsScenariosSetting
buffered data is written to
diskApplication fails with possible loss
of multiple buffered write requests if
failure occurs before buffered data is
written to disk
Application fails with possible loss of
multiple buffered write requests if failure
Single DP2 processor failure System
failure (or double DP2 processor
failure) Application processor failure
DP2BUFFERED (the same behavior as
legacy OSS file caching turned off
[OSSCACHING OFF]) occurs before buffered data is written
to diskApplication fails with possible
loss of multiple buffered write requests
if failure occurs before buffered data is
written to diskApplication fails with
possible loss of a single write request
if failure occurs during the write request
Application fails with possible loss of
multiple buffered write requests if failure
Single DP2 processor failure System
failure (or double DP2 processor
failure) Application processor failure
OSSBUFFERED (the same behavior as
legacy OSS file caching turned on
[OSSCACHING ON]) occurs before buffered data is written
to diskApplication fails with possible
loss of multiple buffered write requests
if failure occurs before buffered data is
written to diskApplication fails with
possible loss of multiple buffered write
requests if failure occurs before buffered
data is written to disk
Changing Fileset Catalog Buffering
The value used for the BUFFERED option can have a dramatic effect on application performance
when there are a lot of calls to OSS file system functions that cause fileset catalog updates; such
calls include: creat(), unlink(), rename(), chmod(), chown(), mkdir(), and so on. The
possible values of the BUFFERED option are, in order of increasing buffer usage:
When to Use ItValue
An OSS name server writes a record in the PXLOG file as part of each fileset catalog operation. When
both processes of a OSS name server process pair involved in the operation fail, recovering from a
NONE
partially completed operation is fast because it is based on the PXLOG file entry.This option is provides
the slowest performance for fileset catalog updates but provides the fastest recovery from complete
OSS name server failure.
An OSS name server does not write PXLOG records; it checkpoints these records to its backup process.
The backup process of an OSS name server keeps these records in its memory and uses them to
LOG
recover partially completed operations in the event of a failure of an OSS name server primary process.
If total failure of an OSS name server occurs, FSCK is automatically run against the fileset during the
fileset remounting operation.This option provides better performance for fileset catalog updatesat the
expense of slower recovery in the event of complete OSS name server failure. You can control the
relative likelihood of needing fileset repair, and therefore the relative speed of recovery, by adjusting
the MAXDIRTYINODETIME attribute for the fileset.
The OSS name server does not write PXLOG records but rather checkpoints these records to its backup
process. The backup process keeps these records in its memory and uses them to recover partially
CREATE
completed operations in the event of a failure of the OSS name server primary process. If total failure
of the OSS name server occurs, FSCK is automatically run against the fileset during the fileset
remounting operation.The disk process does not write new file labels immediately but rather defers
these label writes until it has nothing else to do.This option provides the best performance for fileset
catalog updatesbut limits the fileset to one disk volume and has the potential for lost files in the event
of a double-disk process failure. See “Creating a Unique Fileset” (page 140) for additional considerations
when you use BUFFERED CREATE.
154 Managing Filesets