The syncdir mount option can be used for cluster file systems that use UFS as the underlying file system. However, there is a significant performance improvement if you do not specify syncdir. If you specify syncdir, the writes are guaranteed to be POSIX compliant. If you do not, you will have the same behavior that is seen with NFS file systems. For example, under some cases, without syncdir, you would not discover an out of space condition until you close a file. With syncdir (and POSIX behavior), the out of space condition would have been discovered during the write operation. The cases in which you could have problems if you do not specify syncdir are rare, so we recommend that you do not specify it and receive the performance benefit.
VxFS does not have a mount-option equivalent to the syncdir mount option for UFS. VxFS behavior is the same as for UFS when the syncdir mount option is not specified.
See File Systems FAQs for frequently asked questions about global devices and cluster file systems.