Exam DES-1423 topic 1 question 19 discussion

An Isilon administrator has four H600 nodes and eight A2000 nodes in the cluster. The file pool policy is configured to have all new data written to the H600 nodes. After a few weeks, the administrator has some concerns about the available capacity on the H600 nodes.
Which feature should be configured to accept writes, even after the H600 nodes become full?