Veritas™ File System 5.0.1 Administrator's Guide

■ The mincache=direct, mincache=unbuffered, and mincache=dsync modes
also flush file data on close as mincache=closesync does.
Because the mincache=direct, mincache=unbuffered, and mincache=dsync modes
change non-synchronous I/O to synchronous I/O, throughput can substantially
degrade for small to medium size files with most applications. Since the VX_DIRECT
and VX_UNBUFFERED advisories do not allow any caching of data, applications that
normally benefit from caching for reads usually experience less degradation with
the mincache=dsync mode. mincache=direct and mincache=unbuffered require
significantly less CPU time than buffered I/O.
If performance is more important than data integrity, you can use the
mincache=tmpcache mode. The mincache=tmpcache mode disables special delayed
extending write handling, trading off less integrity for better performance. Unlike
the other mincache modes, tmpcache does not flush the file to disk the file is
closed. When the mincache=tmpcache option is used, bad data can appear in a file
that was being extended when a crash occurred.
The convosync mode
The convosync (convert osync) mode has the following suboptions:
■ convosync=closesync
Note: The convosync=closesync mode converts synchronous and data
synchronous writes to non-synchronous writes and flushes the changes to the
file to disk when the file is closed.
■ convosync=delay
■ convosync=direct
■ convosync=dsync
Note: The convosync=dsync option violates POSIX guarantees for synchronous
I/O.
■ convosync=unbuffered
The convosync=delay mode causes synchronous and data synchronous writes to
be delayed rather than to take effect immediately. No special action is performed
when closing a file. This option effectively cancels any data integrity guarantees
normally provided by opening a file with O_SYNC.
39VxFS performance: creating, mounting, and tuning file systems
Mounting a VxFS file system