diff --git a/hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/fs/SpaceUsageSource.java b/hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/fs/SpaceUsageSource.java
index 7ef5c4f58230..2295d1c71e47 100644
--- a/hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/fs/SpaceUsageSource.java
+++ b/hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/fs/SpaceUsageSource.java
@@ -28,7 +28,7 @@
 @InterfaceAudience.Private
 @InterfaceStability.Evolving
 public interface SpaceUsageSource {
-  SpaceUsageSource UNKNOWN = new Fixed(0, 0, 0);
+  Fixed UNKNOWN = new Fixed(0, 0, 0);
 
   /**
    * @return space usage in bytes
@@ -41,7 +41,7 @@ public interface SpaceUsageSource {
 
   long getAvailable();
 
-  default SpaceUsageSource snapshot() {
+  default Fixed snapshot() {
     return new Fixed(getCapacity(), getAvailable(), getUsedSpace());
   }
 
@@ -77,7 +77,7 @@ public long getUsedSpace() {
     }
 
     @Override
-    public SpaceUsageSource snapshot() {
+    public Fixed snapshot() {
       return this; // immutable
     }
 
diff --git a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/volume/MutableVolumeSet.java b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/volume/MutableVolumeSet.java
index c704245be543..852a6f77299c 100644
--- a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/volume/MutableVolumeSet.java
+++ b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/volume/MutableVolumeSet.java
@@ -57,7 +57,7 @@ public class MutableVolumeSet implements VolumeSet {
    * Maintains a map of all active volumes in the DataNode.
    * Each volume has one-to-one mapping with a volumeInfo object.
    */
-  private Map<String, StorageVolume> volumeMap;
+  private final Map<String, StorageVolume> volumeMap = new ConcurrentHashMap<>();
   /**
    * Maintains a map of volumes which have failed. The keys in this map and
    * {@link #volumeMap} are mutually exclusive.
@@ -147,7 +147,6 @@ public StorageVolumeChecker getVolumeChecker() {
    * Add DN volumes configured through ConfigKeys to volumeMap.
    */
   private void initializeVolumeSet() throws IOException {
-    volumeMap = new ConcurrentHashMap<>();
     failedVolumeMap = new ConcurrentHashMap<>();
     volumeStateMap = new EnumMap<>(StorageType.class);
 
@@ -452,8 +451,9 @@ public Map<String, StorageVolume> getVolumeMap() {
   }
 
   @VisibleForTesting
-  public void setVolumeMap(Map<String, StorageVolume> map) {
-    this.volumeMap = map;
+  public void setVolumeMapForTesting(Map<String, StorageVolume> map) {
+    volumeMap.clear();
+    volumeMap.putAll(map);
   }
 
   @VisibleForTesting
diff --git a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/volume/StorageVolume.java b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/volume/StorageVolume.java
index 45feede53a1e..b04771b85a2a 100644
--- a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/volume/StorageVolume.java
+++ b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/volume/StorageVolume.java
@@ -468,7 +468,7 @@ public String getVolumeRootDir() {
   }
 
   /** Get current usage of the volume. */
-  public SpaceUsageSource getCurrentUsage() {
+  public SpaceUsageSource.Fixed getCurrentUsage() {
     return volumeUsage != null ? volumeUsage.getCurrentUsage() : SpaceUsageSource.UNKNOWN;
   }
 
diff --git a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/volume/VolumeUsage.java b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/volume/VolumeUsage.java
index f67ccfaef72b..75dcf3b46de0 100644
--- a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/volume/VolumeUsage.java
+++ b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/volume/VolumeUsage.java
@@ -107,7 +107,7 @@ public class VolumeUsage {
     Preconditions.assertTrue(reservedInBytes >= 0, reservedInBytes + " < 0");
   }
 
-  SpaceUsageSource realUsage() {
+  SpaceUsageSource.Fixed realUsage() {
     return source.snapshot();
   }
 
@@ -123,9 +123,8 @@ SpaceUsageSource realUsage() {
    * </pre>
    * B) avail = fsAvail - Max(reserved - other, 0);
    */
-  public SpaceUsageSource getCurrentUsage() {
-    SpaceUsageSource real = realUsage();
-
+  public SpaceUsageSource.Fixed getCurrentUsage() {
+    final SpaceUsageSource.Fixed real = realUsage();
     return reservedInBytes == 0
         ? real
         : new SpaceUsageSource.Fixed(
diff --git a/hadoop-hdds/container-service/src/test/java/org/apache/hadoop/ozone/container/upgrade/TestDatanodeUpgradeToSchemaV3.java b/hadoop-hdds/container-service/src/test/java/org/apache/hadoop/ozone/container/upgrade/TestDatanodeUpgradeToSchemaV3.java
index 28cf1c831acf..abee873cc8a8 100644
--- a/hadoop-hdds/container-service/src/test/java/org/apache/hadoop/ozone/container/upgrade/TestDatanodeUpgradeToSchemaV3.java
+++ b/hadoop-hdds/container-service/src/test/java/org/apache/hadoop/ozone/container/upgrade/TestDatanodeUpgradeToSchemaV3.java
@@ -556,7 +556,7 @@ public void testFinalizeFailure(boolean schemaV3Enabled) throws Exception {
         createDbStore(any());
     Map volumeMap = new HashMap<String, StorageVolume>();
     volumeMap.put(dataVolume.getStorageID(), volume);
-    dsm.getContainer().getVolumeSet().setVolumeMap(volumeMap);
+    dsm.getContainer().getVolumeSet().setVolumeMapForTesting(volumeMap);
 
     // Finalize will fail because of DB creation failure
     try {
diff --git a/hadoop-hdds/framework/src/main/java/org/apache/hadoop/hdds/fs/CachingSpaceUsageSource.java b/hadoop-hdds/framework/src/main/java/org/apache/hadoop/hdds/fs/CachingSpaceUsageSource.java
index 4aee3a1484e5..27e6f7d4144f 100644
--- a/hadoop-hdds/framework/src/main/java/org/apache/hadoop/hdds/fs/CachingSpaceUsageSource.java
+++ b/hadoop-hdds/framework/src/main/java/org/apache/hadoop/hdds/fs/CachingSpaceUsageSource.java
@@ -50,7 +50,7 @@ public class CachingSpaceUsageSource implements SpaceUsageSource {
   private long cachedUsedSpace;
   private long cachedAvailable;
   private long cachedCapacity;
-  private SpaceUsageSource cachedUsage;
+  private Fixed cachedUsage;
   private final Duration refresh;
   private final SpaceUsageSource source;
   private final SpaceUsagePersistence persistence;
@@ -102,7 +102,7 @@ public long getUsedSpace() {
   }
 
   @Override
-  public SpaceUsageSource snapshot() {
+  public Fixed snapshot() {
     try (AutoCloseableLock ignored = lock.readLock(null, null)) {
       if (cachedUsage != null) {
         return cachedUsage;