diff --git a/hbase-client/src/main/java/org/apache/hadoop/hbase/client/ClusterConnection.java b/hbase-client/src/main/java/org/apache/hadoop/hbase/client/ClusterConnection.java
index c813bae6665..f23eb82eacc 100644
--- a/hbase-client/src/main/java/org/apache/hadoop/hbase/client/ClusterConnection.java
+++ b/hbase-client/src/main/java/org/apache/hadoop/hbase/client/ClusterConnection.java
@@ -21,7 +21,6 @@ package org.apache.hadoop.hbase.client;
 import java.io.IOException;
 import java.util.List;
 
-import org.apache.hadoop.hbase.classification.InterfaceAudience;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.hbase.HRegionLocation;
 import org.apache.hadoop.hbase.MasterNotRunningException;
@@ -306,4 +305,9 @@ public interface ClusterConnection extends HConnection {
    */
   public MetricsConnection getConnectionMetrics();
 
+  /**
+   * @return true when this connection uses a {@link org.apache.hadoop.hbase.codec.Codec} and so
+   *         supports cell blocks.
+   */
+  boolean hasCellBlockSupport();
 }
diff --git a/hbase-client/src/main/java/org/apache/hadoop/hbase/client/ConnectionAdapter.java b/hbase-client/src/main/java/org/apache/hadoop/hbase/client/ConnectionAdapter.java
index b42593e9d8b..7a18ea536ba 100644
--- a/hbase-client/src/main/java/org/apache/hadoop/hbase/client/ConnectionAdapter.java
+++ b/hbase-client/src/main/java/org/apache/hadoop/hbase/client/ConnectionAdapter.java
@@ -469,4 +469,9 @@ abstract class ConnectionAdapter implements ClusterConnection {
   public ClientBackoffPolicy getBackoffPolicy() {
     return wrappedConnection.getBackoffPolicy();
   }
+
+  @Override
+  public boolean hasCellBlockSupport() {
+    return wrappedConnection.hasCellBlockSupport();
+  }
 }
diff --git a/hbase-client/src/main/java/org/apache/hadoop/hbase/client/ConnectionManager.java b/hbase-client/src/main/java/org/apache/hadoop/hbase/client/ConnectionManager.java
index 7a298e20fc6..5aa604da9a1 100644
--- a/hbase-client/src/main/java/org/apache/hadoop/hbase/client/ConnectionManager.java
+++ b/hbase-client/src/main/java/org/apache/hadoop/hbase/client/ConnectionManager.java
@@ -57,8 +57,6 @@ import org.apache.hadoop.hbase.HTableDescriptor;
 import org.apache.hadoop.hbase.MasterNotRunningException;
 import org.apache.hadoop.hbase.MetaTableAccessor;
 import org.apache.hadoop.hbase.RegionLocations;
-import org.apache.hadoop.hbase.RegionTooBusyException;
-import org.apache.hadoop.hbase.RetryImmediatelyException;
 import org.apache.hadoop.hbase.ServerName;
 import org.apache.hadoop.hbase.TableName;
 import org.apache.hadoop.hbase.TableNotEnabledException;
@@ -73,7 +71,6 @@ import org.apache.hadoop.hbase.client.backoff.ClientBackoffPolicyFactory;
 import org.apache.hadoop.hbase.client.coprocessor.Batch;
 import org.apache.hadoop.hbase.exceptions.ClientExceptionsUtil;
 import org.apache.hadoop.hbase.exceptions.RegionMovedException;
-import org.apache.hadoop.hbase.exceptions.RegionOpeningException;
 import org.apache.hadoop.hbase.ipc.RpcClient;
 import org.apache.hadoop.hbase.ipc.RpcClientFactory;
 import org.apache.hadoop.hbase.ipc.RpcControllerFactory;
@@ -184,7 +181,6 @@ import org.apache.hadoop.hbase.protobuf.generated.MasterProtos.TruncateTableRequ
 import org.apache.hadoop.hbase.protobuf.generated.MasterProtos.TruncateTableResponse;
 import org.apache.hadoop.hbase.protobuf.generated.MasterProtos.UnassignRegionRequest;
 import org.apache.hadoop.hbase.protobuf.generated.MasterProtos.UnassignRegionResponse;
-import org.apache.hadoop.hbase.quotas.ThrottlingException;
 import org.apache.hadoop.hbase.regionserver.RegionServerStoppedException;
 import org.apache.hadoop.hbase.security.User;
 import org.apache.hadoop.hbase.security.UserProvider;
@@ -2620,6 +2616,11 @@ class ConnectionManager {
     public boolean isManaged() {
       return managed;
     }
+
+    @Override
+    public boolean hasCellBlockSupport() {
+      return this.rpcClient.hasCellBlockSupport();
+    }
   }
 
   /**
diff --git a/hbase-client/src/main/java/org/apache/hadoop/hbase/client/MultiServerCallable.java b/hbase-client/src/main/java/org/apache/hadoop/hbase/client/MultiServerCallable.java
index 9dbebb45f17..f02d14df332 100644
--- a/hbase-client/src/main/java/org/apache/hadoop/hbase/client/MultiServerCallable.java
+++ b/hbase-client/src/main/java/org/apache/hadoop/hbase/client/MultiServerCallable.java
@@ -22,7 +22,6 @@ import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
 
-import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.hbase.CellScannable;
 import org.apache.hadoop.hbase.CellUtil;
 import org.apache.hadoop.hbase.DoNotRetryIOException;
@@ -152,11 +151,8 @@ class MultiServerCallable<R> extends RegionServerCallable<MultiResponse> impleme
     // This is not exact -- the configuration could have changed on us after connection was set up
     // but it will do for now.
     HConnection connection = getConnection();
-    if (connection == null) return true; // Default is to do cellblocks.
-    Configuration configuration = connection.getConfiguration();
-    if (configuration == null) return true;
-    String codec = configuration.get(HConstants.RPC_CODEC_CONF_KEY, "");
-    return codec != null && codec.length() > 0;
+    if (!(connection instanceof ClusterConnection)) return true; // Default is to do cellblocks.
+    return ((ClusterConnection) connection).hasCellBlockSupport();
   }
 
   @Override
diff --git a/hbase-client/src/main/java/org/apache/hadoop/hbase/ipc/AbstractRpcClient.java b/hbase-client/src/main/java/org/apache/hadoop/hbase/ipc/AbstractRpcClient.java
index e33ef3a1479..a53fb707082 100644
--- a/hbase-client/src/main/java/org/apache/hadoop/hbase/ipc/AbstractRpcClient.java
+++ b/hbase-client/src/main/java/org/apache/hadoop/hbase/ipc/AbstractRpcClient.java
@@ -149,6 +149,11 @@ public abstract class AbstractRpcClient implements RpcClient {
     }
   }
 
+  @Override
+  public boolean hasCellBlockSupport() {
+    return this.codec != null;
+  }
+
   /**
    * Encapsulate the ugly casting and RuntimeException conversion in private method.
    * @param conf configuration
diff --git a/hbase-client/src/main/java/org/apache/hadoop/hbase/ipc/RpcClient.java b/hbase-client/src/main/java/org/apache/hadoop/hbase/ipc/RpcClient.java
index cf689f5860c..540e224bdfe 100644
--- a/hbase-client/src/main/java/org/apache/hadoop/hbase/ipc/RpcClient.java
+++ b/hbase-client/src/main/java/org/apache/hadoop/hbase/ipc/RpcClient.java
@@ -83,4 +83,10 @@ import java.io.IOException;
    * using this client.
    */
   @Override public void close();
+
+  /**
+   * @return true when this client uses a {@link org.apache.hadoop.hbase.codec.Codec} and so
+   *         supports cell blocks.
+   */
+  boolean hasCellBlockSupport();
 }
\ No newline at end of file
diff --git a/hbase-client/src/main/java/org/apache/hadoop/hbase/protobuf/ProtobufUtil.java b/hbase-client/src/main/java/org/apache/hadoop/hbase/protobuf/ProtobufUtil.java
index e19f2f0939a..6fa17c95042 100644
--- a/hbase-client/src/main/java/org/apache/hadoop/hbase/protobuf/ProtobufUtil.java
+++ b/hbase-client/src/main/java/org/apache/hadoop/hbase/protobuf/ProtobufUtil.java
@@ -73,7 +73,6 @@ import org.apache.hadoop.hbase.filter.ByteArrayComparable;
 import org.apache.hadoop.hbase.filter.Filter;
 import org.apache.hadoop.hbase.io.LimitInputStream;
 import org.apache.hadoop.hbase.io.TimeRange;
-import org.apache.hadoop.hbase.protobuf.generated.RPCProtos;
 import org.apache.hadoop.hbase.protobuf.generated.AccessControlProtos;
 import org.apache.hadoop.hbase.protobuf.generated.AccessControlProtos.AccessControlService;
 import org.apache.hadoop.hbase.protobuf.generated.AdminProtos.AdminService;
@@ -1206,10 +1205,6 @@ public final class ProtobufUtil {
         valueBuilder.setValue(ByteStringer.wrap(
             cell.getValueArray(), cell.getValueOffset(), cell.getValueLength()));
         valueBuilder.setTimestamp(cell.getTimestamp());
-        if(cell.getTagsLength() > 0) {
-          valueBuilder.setTags(ByteStringer.wrap(cell.getTagsArray(), cell.getTagsOffset(),
-              cell.getTagsLength()));
-        }
         if (type == MutationType.DELETE || (type == MutationType.PUT && CellUtil.isDelete(cell))) {
           KeyValue.Type keyValueType = KeyValue.Type.codeToType(cell.getTypeByte());
           valueBuilder.setDeleteType(toDeleteType(keyValueType));
diff --git a/hbase-client/src/main/java/org/apache/hadoop/hbase/protobuf/RequestConverter.java b/hbase-client/src/main/java/org/apache/hadoop/hbase/protobuf/RequestConverter.java
index 96f5d9ec0a8..be2bab25baa 100644
--- a/hbase-client/src/main/java/org/apache/hadoop/hbase/protobuf/RequestConverter.java
+++ b/hbase-client/src/main/java/org/apache/hadoop/hbase/protobuf/RequestConverter.java
@@ -21,8 +21,6 @@ import java.io.IOException;
 import java.util.List;
 import java.util.regex.Pattern;
 
-import org.apache.hadoop.hbase.util.ByteStringer;
-
 import org.apache.hadoop.hbase.classification.InterfaceAudience;
 import org.apache.hadoop.hbase.CellScannable;
 import org.apache.hadoop.hbase.DoNotRetryIOException;
@@ -680,8 +678,15 @@ public final class RequestConverter {
         cells.add(i);
         builder.addAction(actionBuilder.setMutation(ProtobufUtil.toMutationNoData(
           MutationType.INCREMENT, i, mutationBuilder, action.getNonce())));
+      } else if (row instanceof RegionCoprocessorServiceExec) {
+        RegionCoprocessorServiceExec exec = (RegionCoprocessorServiceExec) row;
+        builder.addAction(actionBuilder.setServiceCall(ClientProtos.CoprocessorServiceCall
+            .newBuilder().setRow(ByteStringer.wrap(exec.getRow()))
+            .setServiceName(exec.getMethod().getService().getFullName())
+            .setMethodName(exec.getMethod().getName())
+            .setRequest(exec.getRequest().toByteString())));
       } else if (row instanceof RowMutations) {
-        continue; // ignore RowMutations
+        throw new UnsupportedOperationException("No RowMutations in multi calls; use mutateRow");
       } else {
         throw new DoNotRetryIOException("Multi doesn't support " + row.getClass().getName());
       }
diff --git a/hbase-server/src/test/java/org/apache/hadoop/hbase/security/access/TestAccessController.java b/hbase-server/src/test/java/org/apache/hadoop/hbase/security/access/TestAccessController.java
index fcdd334d9a1..75e69b67b2e 100644
--- a/hbase-server/src/test/java/org/apache/hadoop/hbase/security/access/TestAccessController.java
+++ b/hbase-server/src/test/java/org/apache/hadoop/hbase/security/access/TestAccessController.java
@@ -2505,30 +2505,6 @@ public class TestAccessController extends SecureTestUtil {
     }
   }
 
-  @Test (timeout=180000)
-  public void testReservedCellTags() throws Exception {
-    AccessTestAction putWithReservedTag = new AccessTestAction() {
-      @Override
-      public Object run() throws Exception {
-        try(Connection conn = ConnectionFactory.createConnection(conf);
-            Table t = conn.getTable(TEST_TABLE);) {
-          KeyValue kv = new KeyValue(TEST_ROW, TEST_FAMILY, TEST_QUALIFIER,
-            HConstants.LATEST_TIMESTAMP, HConstants.EMPTY_BYTE_ARRAY,
-            new Tag[] { new Tag(AccessControlLists.ACL_TAG_TYPE,
-              ProtobufUtil.toUsersAndPermissions(USER_OWNER.getShortName(),
-                new Permission(Permission.Action.READ)).toByteArray()) });
-          t.put(new Put(TEST_ROW).add(kv));
-        }
-        return null;
-      }
-    };
-
-    // Current user is superuser
-    verifyAllowed(putWithReservedTag, User.getCurrent());
-    // No other user should be allowed
-    verifyDenied(putWithReservedTag, USER_OWNER, USER_ADMIN, USER_CREATE, USER_RW, USER_RO);
-  }
-
   @Test (timeout=180000)
   public void testSetQuota() throws Exception {
     AccessTestAction setUserQuotaAction = new AccessTestAction() {