Open System Services Programmer's Guide

FTIOMODE, NORMALIOMODE, Performance, and Fault Tolerance
The value used for the FTIOMODE and NORMALIOMODE options affect application performance
and fault tolerance. Fault tolerance for files opened without using the O_SYNC bit is controlled by
the NORMALIOMODE option setting; fault tolerance for files opened using the O_SYNC bit is
controlled by the FTIOMODE option setting.
NOTE: HP recommends that the S_NONSTOP extension not be used in new applications. The
S_NONSTOP extension is ignored on nodes running J-series RVUs or an RVU more recent than
G06.26 or H06.03; the standard O_SYNC feature used with the FTIOMODE attribute provides
better data integrity and improved performance.
The attribute settings for NORMALIOMODE are, from highest to lowest fault tolerance and from
lowest to highest performance:
UNBUFFEREDCP
DP2BUFFEREDCP
OSSBUFFEREDCP
DP2BUFFERED (Same as legacy OSS file caching turned off [OSSCACHING OFF])
OSSBUFFERED (Same as legacy OSS file caching turned on [OSSCACHING ON])
If NORMALIOMODE is not specified, the default behavior is OSSBUFFEREDCP.
The FTIOMODE settings are a subset of the NORMALIOMODE settings. The setting used for the
FTIOMODE attribute of a specific fileset must have a fault-tolerance level at least as high as that
of the NORMALIOMODE attribute setting for the fileset. The attribute settings for FTIOMODE are,
from highest to lowest fault tolerance and from lowest to highest performance:
UNBUFFEREDCP
DP2BUFFEREDCP
OSSBUFFEREDCP
If FTIOMODE is not specified, the default behavior is UNBUFFEREDCP.
File caching and buffering affect the data integrity of a file and file transfer speed as described in
Table 7.
Table 7 I/O Buffering, Fault Tolerance, and Performance
Fault Tolerance and PerformanceBehaviorNORMALIOMODE or
FTIOMODE Attribute Value
Provides maximum fault tolerance but with
reduced performance.
Uses unbuffered input/output with
checkpointing.
UNBUFFEREDCP
Provides fault tolerance for single failures,
with better performance than
UNBUFFEREDCP.
Uses disk-process-buffered input/output with
checkpointing.
DP2 buffers file data and checkpoints the
file state to its backup process to ensure
recovery from single failures.
DP2BUFFEREDCP
Provides fault tolerance for single failures,
with better performance than
DP2BUFFEREDCP.
Uses OSS-buffered input/output with
checkpointing.
OSS filesystem processes and DP2 share
responsibility for buffering file data; OSS
OSSBUFFEREDCP
provides the buffering whenever possible.
DP2 buffers file data and checkpoints the
file state to its backup process to ensure
recovery from single failures.
Provides no fault tolerance, but better
performance than DPBUFFEREDCP.
Uses disk-process-buffered input/output
without checkpointing.
DP2BUFFERED
Provides no fault tolerance, but better
performance than OSSBUFFEREDCP.
Uses OSS-buffered input/output without
checkpointing.
OSSBUFFERED
88 Managing Files