diff --git a/hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/om/helpers/OMRatisHelper.java b/hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/om/helpers/OMRatisHelper.java
index a483fbc6870..af4075ddef7 100644
--- a/hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/om/helpers/OMRatisHelper.java
+++ b/hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/om/helpers/OMRatisHelper.java
@@ -53,9 +53,16 @@ public static OMRequest convertByteStringToOMRequest(ByteString bytes) throws IO
     return OMRequest.parseFrom(new ByteBufferInputStream(buffer));
   }
 
-  /** Convert the given proto 2 response to a proto 3 {@link ByteString}. */
+  /**
+   * Convert the given proto 2 response to a Ratis {@link Message}.
+   * <p>
+   * The response is serialized eagerly so that the returned {@link Message} holds only the serialized bytes.
+   * Ratis keeps the reply {@link Message} in its retry cache (on the leader and on every follower) for
+   * {@code ozone.om.ratis.server.retry.cache.timeout}, so a lazily serializing {@link Message} would retain
+   * the whole parsed {@link OMResponse} tree for that long, which dominates OM heap under a write burst.
+   */
   public static Message convertResponseToMessage(OMResponse response) {
-    return () -> UnsafeByteOperations.unsafeWrap(response.toByteString().asReadOnlyByteBuffer());
+    return Message.valueOf(UnsafeByteOperations.unsafeWrap(response.toByteArray()));
   }
 
   /** Convert the given proto 3 {@link ByteString} to a proto 2 response. */
diff --git a/hadoop-ozone/common/src/test/java/org/apache/hadoop/ozone/om/helpers/TestOMRatisHelper.java b/hadoop-ozone/common/src/test/java/org/apache/hadoop/ozone/om/helpers/TestOMRatisHelper.java
new file mode 100644
index 00000000000..6a320eedb6b
--- /dev/null
+++ b/hadoop-ozone/common/src/test/java/org/apache/hadoop/ozone/om/helpers/TestOMRatisHelper.java
@@ -0,0 +1,106 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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 org.apache.hadoop.ozone.om.helpers;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertSame;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+import org.apache.hadoop.hdds.protocol.proto.HddsProtos.ReplicationFactor;
+import org.apache.hadoop.hdds.protocol.proto.HddsProtos.ReplicationType;
+import org.apache.hadoop.ozone.protocol.proto.OzoneManagerProtocolProtos.CreateKeyResponse;
+import org.apache.hadoop.ozone.protocol.proto.OzoneManagerProtocolProtos.KeyInfo;
+import org.apache.hadoop.ozone.protocol.proto.OzoneManagerProtocolProtos.OMResponse;
+import org.apache.hadoop.ozone.protocol.proto.OzoneManagerProtocolProtos.Status;
+import org.apache.hadoop.ozone.protocol.proto.OzoneManagerProtocolProtos.Type;
+import org.apache.ratis.protocol.Message;
+import org.apache.ratis.protocol.RaftClientReply;
+import org.apache.ratis.protocol.RaftPeerId;
+import org.apache.ratis.thirdparty.com.google.protobuf.ByteString;
+import org.apache.ratis.thirdparty.com.google.protobuf.UnsafeByteOperations;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Test for {@link OMRatisHelper}.
+ */
+class TestOMRatisHelper {
+
+  private static OMResponse createKeyResponse() {
+    return OMResponse.newBuilder()
+        .setCmdType(Type.CreateKey)
+        .setStatus(Status.OK)
+        .setSuccess(true)
+        .setCreateKeyResponse(CreateKeyResponse.newBuilder()
+            .setKeyInfo(KeyInfo.newBuilder()
+                .setVolumeName("vol")
+                .setBucketName("buck")
+                .setKeyName("key")
+                .setDataSize(4096)
+                .setType(ReplicationType.RATIS)
+                .setFactor(ReplicationFactor.THREE)
+                .setCreationTime(1)
+                .setModificationTime(2)
+                .build())
+            .setID(42)
+            .setOpenVersion(1)
+            .build())
+        .build();
+  }
+
+  /**
+   * The reply {@link Message} is kept by the Ratis retry cache for the whole retry-cache timeout,
+   * so it must hold the serialized bytes only, not the parsed {@link OMResponse} tree.
+   * Serializing eagerly makes {@link Message#getContent()} return the very same instance every time.
+   */
+  @Test
+  void convertResponseToMessageSerializesEagerly() {
+    final OMResponse response = createKeyResponse();
+    final Message message = OMRatisHelper.convertResponseToMessage(response);
+
+    final ByteString content = message.getContent();
+    assertSame(content, message.getContent());
+    assertEquals(UnsafeByteOperations.unsafeWrap(response.toByteString().asReadOnlyByteBuffer()), content);
+  }
+
+  /**
+   * A retried request answered from the retry cache must get back exactly the original response.
+   */
+  @Test
+  void convertResponseToMessageRoundTrips() throws Exception {
+    final OMResponse response = createKeyResponse();
+    final Message message = OMRatisHelper.convertResponseToMessage(response);
+
+    assertEquals(response, OMRatisHelper.convertByteStringToOMResponse(message.getContent()));
+  }
+
+  /**
+   * The leader stamps its node id on the reply it returns to the client; the result must be the
+   * cached response with that one field set.
+   */
+  @Test
+  void getOMResponseFromRaftClientReplySetsLeaderId() throws Exception {
+    final OMResponse response = createKeyResponse();
+    final RaftClientReply reply = mock(RaftClientReply.class);
+    when(reply.getMessage()).thenReturn(OMRatisHelper.convertResponseToMessage(response));
+
+    assertEquals(response, OMRatisHelper.getOMResponseFromRaftClientReply(reply, null));
+    assertEquals(OMResponse.newBuilder(response).setLeaderOMNodeId("om1").build(),
+        OMRatisHelper.getOMResponseFromRaftClientReply(reply, RaftPeerId.valueOf("om1")));
+  }
+}