Veritas File System 5.1 SP1 Administrator"s Guide (5900-1499, April 2011)

■ 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.
See the open(2), fcntl(2), and vxfsio(7) manual pages.
Warning: Be very careful when using the convosync=closesync or
convosync=delay mode because they actually change synchronous I/O into
non-synchronous I/O. Applications that use synchronous I/O for data reliability
may fail if the system crashes and synchronously written data is lost.
The convosync=dsync mode converts synchronous writes to data synchronous
writes.
As with closesync, the direct, unbuffered, and dsync modes flush changes to
the file to disk when it is closed. These modes can be used to speed up applications
that use synchronous I/O. Many applications that are concerned with data integrity
specify the O_SYNC fcntl in order to write the file data synchronously. However,
this has the undesirable side effect of updating inode times and therefore slowing
down performance. The convosync=dsync, convosync=unbuffered, and
convosync=direct modes alleviate this problem by allowing applications to take
advantage of synchronous writes without modifying inode times as well.
Before using convosync=dsync, convosync=unbuffered, or convosync=direct,
make sure that all applications that use the file system do not require synchronous
inode time updates for O_SYNC writes.
The ioerror mode
This mode sets the policy for handling I/O errors on a mounted file system. I/O
errors can occur while reading or writing file data or metadata. The file system
can respond to these I/O errors either by halting or by gradually degrading. The
ioerror option provides five policies that determine how the file system responds
to the various errors. All policies limit data corruption, either by stopping the file
system or by marking a corrupted inode as bad.
VxFS performance: creating, mounting, and tuning file systems
Mounting a VxFS file system
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