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

98 Chapter5
Performance and Tuning
Choosing Mount Options
Since 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, the
mincache=tmpcache mode may be used. 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 this
option is used, garbage may appear in a file that was being extended
when a crash occurred.
convosync
NOTE Use of the convosync=dsync option violates POSIX guarantees for
synchronous I/O.
The “convert osync” (convosync) mode has five suboptions:
convosync=closesync, convosync=direct, convosync=dsync,
convosync=unbuffered, and convosync=delay.
NOTE The convosync option is available only with the HP OnLineJFS product.
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.
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. See open(2), fcntl(2), and vxfsio(7) for more information on
O_SYNC.