options zfs zfs_dirty_data_max_max=[default 4G?]
, could possibly help if the write during a txg period (default 5 secs) if accumualted data is more that default.
Needs to be set at module load.
options zfs zfs_dirty_data_max=[can cap the max_max dynamically]
Hint: Set data_max_max high and cap with data_max dynamically.