Veritas File System 5.0 Administrator's Guide (September 2006)

mincache=closesync
mincache=direct
mincache=dsync
mincache=unbuffered
mincache=tmpcache
The mincache=closesync mode is useful in desktop environments where users
are likely to shut off the power on the machine without halting it first. In this
mode, any changes to the file are flushed to disk when the file is closed.
To improve performance, most file systems do not synchronously update data
and inode changes to disk. If the system crashes, files that have been updated
within the past minute are in danger of losing data. With the mincache=closesync
mode, if the system crashes or is switched off, only open files can lose data. A
mincache=closesync mode file system could be approximately 15 percent slower
than a standard mode VxFS file system, depending on the workload.
The following describes where to use the mincache modes:
The mincache=direct, mincache=unbuffered, and mincache=dsync modes
are used in environments where applications have 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 are 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 are 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, as well as for the requirements for direct I/O.
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
VxFS performance: creating, mounting, and tuning file systems
Choosing mount command options
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