VERITAS File System 4.1 Administrator's Guide

VxFS Performance: Creating, Mounting, and Tuning File Systems
Choosing mount Command Options
Chapter 244
switched off, only files that are currently open can lose data. A mincache=closesync mode
file system should be approximately 15 percent slower than a standard mode VxFS file
system, depending on the workload.
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.