dsync,direct io

The directio and dsync parameters are mutually exclusive. If a device has dsync set to “true,” you cannot set
directio to “true” for this device. To enable directio for a device, you must first reset dsync to “false.”
Direct I/O is always the preferred way.
dsync only applies to operating system files (meaning that it has no effect on "raw" devices used as Sybase disk devices)

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