diff --git a/tests/netflix/test_crdb.py b/tests/netflix/test_crdb.py
index 17aa7a9..b226fca 100644
--- a/tests/netflix/test_crdb.py
+++ b/tests/netflix/test_crdb.py
@@ -1,32 +1,35 @@
 from service_capacity_modeling.capacity_planner import planner
+from service_capacity_modeling.hardware import shapes
 from service_capacity_modeling.interface import CapacityDesires
 from service_capacity_modeling.interface import DataShape
+from service_capacity_modeling.interface import FixedInterval
 from service_capacity_modeling.interface import Interval
 from service_capacity_modeling.interface import QueryPattern
+from service_capacity_modeling.models.common import working_set_from_drive_and_slo
+from service_capacity_modeling.models.org.netflix import nflx_cockroachdb_capacity_model
+from service_capacity_modeling.stats import dist_for_interval
 
-
-def test_crdb_basic():
-    basic = CapacityDesires(
-        service_tier=1,
-        query_pattern=QueryPattern(
-            estimated_read_per_second=Interval(
-                low=100, mid=1000, high=10000, confidence=0.98
-            ),
-            estimated_write_per_second=Interval(
-                low=100, mid=1000, high=10000, confidence=0.98
-            ),
+simple_desire = CapacityDesires(
+    service_tier=1,
+    query_pattern=QueryPattern(
+        estimated_read_per_second=Interval(
+            low=100, mid=1000, high=10000, confidence=0.98
         ),
-        data_shape=DataShape(
-            estimated_state_size_gib=Interval(
-                low=10, mid=100, high=1000, confidence=0.98
-            ),
+        estimated_write_per_second=Interval(
+            low=100, mid=1000, high=10000, confidence=0.98
         ),
-    )
+    ),
+    data_shape=DataShape(
+        estimated_state_size_gib=Interval(low=10, mid=100, high=1000, confidence=0.98),
+    ),
+)
 
+
+def test_crdb_simple():
     plan = planner.plan(
         model_name="org.netflix.cockroachdb",
         region="us-east-1",
-        desires=basic,
+        desires=simple_desire,
     )
 
     lr = plan.least_regret[0]
@@ -44,6 +47,38 @@ def test_crdb_basic():
     assert lr_cluster.count * lr_cluster.instance.cpu >= 4
 
 
+def test_crdb_working_set():
+    ephem = shapes.region("us-east-1").instances["i4i.xlarge"].drive
+    ebs = shapes.region("us-east-1").drives["gp3"]
+    super_slow_drive = ebs.copy(deep=True)
+    # Simulate a very slow drive
+    super_slow_drive.name = "slow"
+    super_slow_drive.read_io_latency_ms = FixedInterval(
+        low=5, mid=8, high=20, confidence=0.9
+    )
+
+    latency_sensitive = nflx_cockroachdb_capacity_model.default_desires(
+        simple_desire, {}
+    )
+    results = {}
+    for drive in (ephem, ebs, super_slow_drive):
+        working_set = working_set_from_drive_and_slo(
+            drive_read_latency_dist=dist_for_interval(drive.read_io_latency_ms),
+            read_slo_latency_dist=dist_for_interval(
+                latency_sensitive.query_pattern.read_latency_slo_ms
+            ),
+            estimated_working_set=None,
+            # CRDB has looser latency SLOs but we still want a lot of the data
+            # hot in cache. Target the 95th percentile of disk latency to
+            # keep in RAM.
+            target_percentile=0.95,
+        ).mid
+        results[drive.name] = working_set
+    assert results["ephem"] < 0.05
+    assert results["gp3"] < 0.05
+    assert results["slow"] > 0.5
+
+
 def test_crdb_footprint():
     space = CapacityDesires(
         service_tier=1,