VERITAS File System 4.1 Administrator's Guide

VxFS Performance: Creating, Mounting, and Tuning File Systems
Choosing mount Command Options
Chapter 2 41
log is written. If a system failure occurs, recent changes may be lost. This mode approximates
traditional UNIX guarantees for correctness in case of system failures. 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 both 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.
tmplog
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
unitialized 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 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 once
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 with delaylog,
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 will expect the persistence guarantees offered by most
other file systems and will experience 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=, and closesync mount options. However, most
commercially available applications will work well with the default VxFS
mount options, including the delaylog mode.