Veritas File System 5.0 AdministratorÆs Guide, HP-UX 11i v3, First Edition, May 2008

most system calls are not persistent until approximately 30 seconds or more after
the call has returned. Fast file system recovery works with this mode.
The rename(2) system call flushes the source file to disk to guarantee the
persistence of the file data before renaming it. In the log and delaylog modes,
the rename is also guaranteed to be persistent when the system call returns. This
benefits shell scripts and programs that try to update a file atomically by writing
the new file contents to a temporary file and then renaming it on top of the target
file.
The tmplog mode
In tmplog mode, the effects of system calls have persistence guarantees that are
similar to those in delaylog mode. In addition, enhanced flushing of delayed
extending writes is disabled, which results in better performance but increases
the chances of data being lost or uninitialized data appearing in a file that was
being actively written at the time of a system failure. This mode is only
recommended for temporary file systems. Fast file system recovery works with
this mode.
Note: The term "effects of system calls" refers to changes to file system data and
metadata caused by the system call, excluding changes to st_atime.
See the stat(2) manual page.
Persistence guarantees
In all logging modes, VxFS is fully POSIX compliant. The effects of the fsync(2)
and fdatasync(2) system calls are guaranteed to be persistent after the calls
return. The persistence guarantees for data or metadata modified by write(2),
writev(2), or pwrite(2) are not affected by the logging mount options. The effects
of these system calls are guaranteed to be persistent only if the O_SYNC, O_DSYNC,
VX_DSYNC, or VX_DIRECT flag, as modified by the convosync= mount option, has
been specified for the file descriptor.
The behavior of NFS servers on a VxFS file system is unaffected by the log and
tmplog mount options, but not delaylog. In all cases except for tmplog, VxFS
complies with the persistency requirements of the NFS v2 and NFS v3 standard.
Unless a UNIX application has been developed specifically for the VxFS file system
in log mode, it expects the persistence guarantees offered by most other file
systems and experiences improved robustness when used with a VxFS file system
mounted in delaylog mode. Applications that expect better persistence guarantees
than that offered by most other file systems can benefit from the log, mincache=,
VxFS performance: creating, mounting, and tuning file systems
Mounting a VxFS file system
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