The flush command in the DM account flushes to disk all memory-resident buffers that are tagged as write-required.
All write-required buffers are periodically flushed to disk in the normal sequence of events, but this command is provided to ensure data integrity at a given moment. In case of an emergency reboot or problems with the system, flush is a safety measure.
The flushing algorithm varies between implementations of D3.
For UNIX: The flush interval is set by the set-flush command. Roughly 10% of the write-required frames are flushed at each activation.
For Windows: The flush interval is set from the D3 Settings tab of the D3 Device Manager (see the D3 System Administration Guide for more information).