The simplest approach would be to create a raidz with the three disks, that would roughly make a 320G pool with 240 GB wasted.
You might also create a 320 G stripe with the smallest disks, and mirror them with the large one, that time 80G are wasted and performance is better.
If you really don't care about performance, you might create two partitions on the large disk, one 160G and one 240G, create a 320G raidz pool with 3x160G and use ditto blocks on the 240G to create a partially redundant 120G pool, total: 440G. Note that the 120G pool won't survive the 400G full disk failure.
Similarly, you might recover 40G from the previously wasted 80G (suggestion #2), total: 360G
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