diff --git a/apis/reaper/v1alpha1/reaper_types.go b/apis/reaper/v1alpha1/reaper_types.go
index c9bbb820f..10663b6bb 100644
--- a/apis/reaper/v1alpha1/reaper_types.go
+++ b/apis/reaper/v1alpha1/reaper_types.go
@@ -32,13 +32,12 @@ import (
 var SingleReplica = int32(1)
 
 const (
+	DeploymentModeSingle = "SINGLE"
+	DeploymentModePerDc  = "PER_DC"
 	ReaperLabel          = "k8ssandra.io/reaper"
 	DefaultKeyspace      = "reaper_db"
 	StorageTypeCassandra = "cassandra"
 	StorageTypeMemory    = "memory"
-	DefaultStorageClass  = "standard"
-	DefaultStorageSize   = "1Gi"
-	DefaultAccessMode    = corev1.ReadWriteOnce
 )
 
 type ReaperTemplate struct {
@@ -242,6 +241,18 @@ type ReaperClusterTemplate struct {
 	DeploymentMode string `json:"deploymentMode,omitempty"`
 }
 
+// EnsureDeploymentMode ensures that a deployment mode is SINGLE if we use a memory storage type. This is to prevent
+// several instances of in-memory Reapers that would interfere with each other.
+func (t *ReaperClusterTemplate) EnsureDeploymentMode() bool {
+	if t.StorageType == StorageTypeMemory {
+		if t.DeploymentMode != DeploymentModeSingle {
+			t.DeploymentMode = DeploymentModeSingle
+			return true
+		}
+	}
+	return false
+}
+
 // CassandraDatacenterRef references the target Cassandra DC that Reaper should manage.
 // TODO this object could be used by Stargate too; which currently cannot locate DCs outside of its own namespace.
 type CassandraDatacenterRef struct {
diff --git a/apis/reaper/v1alpha1/reaper_types_test.go b/apis/reaper/v1alpha1/reaper_types_test.go
new file mode 100644
index 000000000..9acde8cf6
--- /dev/null
+++ b/apis/reaper/v1alpha1/reaper_types_test.go
@@ -0,0 +1,47 @@
+/*
+Copyright 2021.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package v1alpha1
+
+import (
+	"github.com/stretchr/testify/assert"
+	"testing"
+)
+
+func TestEnsureDeploymentMode(t *testing.T) {
+	t.Run("SINGLE forced when memory storage type", func(t *testing.T) {
+		rct := &ReaperClusterTemplate{
+			ReaperTemplate: ReaperTemplate{
+				StorageType: StorageTypeMemory,
+			},
+			DeploymentMode: DeploymentModePerDc,
+		}
+		changed := rct.EnsureDeploymentMode()
+		assert.True(t, changed)
+		assert.Equal(t, DeploymentModeSingle, rct.DeploymentMode)
+	})
+	t.Run("PER_DC kept when using cassandra storage type", func(t *testing.T) {
+		rct := &ReaperClusterTemplate{
+			ReaperTemplate: ReaperTemplate{
+				StorageType: StorageTypeCassandra,
+			},
+			DeploymentMode: DeploymentModePerDc,
+		}
+		changed := rct.EnsureDeploymentMode()
+		assert.False(t, changed)
+		assert.Equal(t, DeploymentModePerDc, rct.DeploymentMode)
+	})
+}
diff --git a/controllers/k8ssandra/reaper.go b/controllers/k8ssandra/reaper.go
index 4145de48b..62cc2cd49 100644
--- a/controllers/k8ssandra/reaper.go
+++ b/controllers/k8ssandra/reaper.go
@@ -18,7 +18,6 @@ package k8ssandra
 
 import (
 	"context"
-
 	"github.com/go-logr/logr"
 	cassdcapi "github.com/k8ssandra/cass-operator/apis/cassandra/v1beta1"
 	api "github.com/k8ssandra/k8ssandra-operator/apis/k8ssandra/v1alpha1"
@@ -97,6 +96,10 @@ func (r *K8ssandraClusterReconciler) reconcileReaper(
 		}
 	}
 
+	if updated := reaperTemplate.EnsureDeploymentMode(); updated {
+		logger.Info("When using 'memory' storage type, Reaper can only be deployed with SINGLE deployment mode")
+	}
+
 	actualReaper := &reaperapi.Reaper{}
 
 	if reaperTemplate != nil {
diff --git a/pkg/reaper/resource.go b/pkg/reaper/resource.go
index d26992cf4..dccb430e8 100644
--- a/pkg/reaper/resource.go
+++ b/pkg/reaper/resource.go
@@ -15,9 +15,6 @@ import (
 )
 
 const (
-	DeploymentModeSingle = "SINGLE"
-	DeploymentModePerDc  = "PER_DC"
-
 	DatacenterAvailabilityEach = "EACH"
 	DatacenterAvailabilityAll  = "ALL"
 )
@@ -104,7 +101,7 @@ func NewReaper(
 // See https://cassandra-reaper.io/docs/usage/multi_dc/.
 // If we have more than one DC, and each DC has its own Reaper instance, use EACH; otherwise, use ALL.
 func computeReaperDcAvailability(kc *k8ssandraapi.K8ssandraCluster) string {
-	if kc.Spec.Reaper.DeploymentMode == DeploymentModeSingle || len(kc.Spec.Cassandra.Datacenters) == 1 {
+	if kc.Spec.Reaper.DeploymentMode == reaperapi.DeploymentModeSingle || len(kc.Spec.Cassandra.Datacenters) == 1 {
 		return DatacenterAvailabilityAll
 	}
 	return DatacenterAvailabilityEach