HP JFS 3.3 and HP OnLineJFS 3.3 VERITAS File System 3.3 System Administrator's Guide

Chapter 5 99
Performance and Tuning
Choosing Mount Options
CAUTION Extreme care should be taken when using the convosync=closesync or
convosync=delay mode because they actually change synchronous I/O
into non-synchronous I/O. This may cause applications that use
synchronous I/O for data reliability to fail if the system crashes and
synchronously written data is lost.
The convosync=direct and convosync=unbuffered mode convert
synchronous and data synchronous reads and writes to direct reads and
writes.
The convosync=dsync mode converts synchronous writes to data
synchronous writes.
As with closesync, the direct, unbuffered, and dsync modes flush
changes to the file to disk when it is closed. These modes can be used to
speed up applications that use synchronous I/O. Many applications that
are concerned with data integrity specify the O_SYNC fcntl in order to
write the file data synchronously. However, this has the undesirable side
effect of updating inode times and therefore slowing down performance.
The convosync=dsync, convosync=unbuffered, and
convosync=direct modes alleviate this problem by allowing
applications to take advantage of synchronous writes without modifying
inode times as well.
NOTE Before using convosync=dsync, convosync=unbuffered, or
convosync=direct, make sure that all applications that use the file
system do not require synchronous inode time updates for O_SYNC writes.
Combining mount Options
Although mount options can be combined arbitrarily, some combinations
do not make sense. The following examples provide some common and
reasonable mount option combinations.
Example 1 - Desktop File System
# mount -F vxfs -o log,mincache=closesync
/dev/dsk/c1t3d0 /mnt