The average amount of time spent on asynchronous writes of data and index pages to disk from the buffer pool for a tablespace. The writes are performed by database manager page cleaners. They are asynchronous in that they occur independently of query processing, in anticipation of the need for space in a buffer pool.
Average asynchronous write time is shown in milliseconds. It provides a measure of the I/O being performed for a tablespace. To see elapsed asynchronous write time, check Pool Async Write Time (msec) in the Tablespace Details tab.