Veritas File System 5.1 SP1 Administrator"s Guide (5900-1499, April 2011)

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.
Logging mode 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=,
and closesync mount options. However, most commercially available applications
work well with the default VxFS mount options, including the delaylog mode.
The logiosize mode
The logiosize=size option enhances the performance of storage devices that
employ a read-modify-write feature. If you specify logiosize when you mount a
file system, VxFS writes the intent log in the least size bytes or a multiple of size
bytes to obtain the maximum performance from such devices.
See the mount_vxfs(1M) manual page.
The values for size can be 1024, 2048, or 4096.
The nodatainlog mode
Use the nodatainlog mode on systems with disks that do not support bad block
revectoring. Usually, a VxFS file system uses the intent log for synchronous writes.
The inode update and the data are both logged in the transaction, so a synchronous
write only requires one disk write instead of two. When the synchronous write
returns to the application, the file system has told the application that the data
37VxFS performance: creating, mounting, and tuning file systems
Mounting a VxFS file system