Veritas File System 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

VxFS Performance: Creating, Mounting, and Tuning File Systems
Choosing mount Command Options
Chapter 2 31
The mincache=direct, mincache=unbuffered, and mincache=dsync modes are used in
environments where applications are experiencing reliability problems caused by the kernel buffering of I/O
and delayed flushing of non-synchronous I/O. The mincache=direct and mincache=unbuffered
modes guarantee that all non-synchronous I/O requests to files will be handled as if the VX_DIRECT or
VX_UNBUFFERED caching advisories had been specified. The mincache=dsync mode guarantees that all
non-synchronous I/O requests to files will be handled as if the VX_DSYNC caching advisory had been
specified. Refer to the vxfsio (7) manual page for explanations of VX_DIRECT, VX_UNBUFFERED, and
VX_DSYNC. 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, there can be a substantial degradation in throughput for small to
medium size files for most applications. Since the VX_DIRECT and VX_UNBUFFERED advisories do not
allow any caching of data, applications that would normally benefit from caching for reads will 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 when
it is closed. When the mincache=tmpcache option is used, bad data can appear in a file that was being
extended when a crash occurred.