IO:DataFileSync

This is the wait event that occurs when a backend process is waiting for a data file to be synchronized to disk.
This is expected during the durable writes, which flushes the dirty pages in the buffers to disk. This typically expected during a checkpoint.

Monitoring

During the checkpoint operation, The checkpointer process is expected to show upto 3% of wait time on this event.
If processes are showing high wait time on this event, It indicates that the storage is slow in synchronizing the data files to disk.