diff --git a/src/main/java/net/openhft/chronicle/map/MultiMapFactory.java b/src/main/java/net/openhft/chronicle/map/MultiMapFactory.java
index ca137ab23..1a615bd24 100644
--- a/src/main/java/net/openhft/chronicle/map/MultiMapFactory.java
+++ b/src/main/java/net/openhft/chronicle/map/MultiMapFactory.java
@@ -21,7 +21,7 @@ package net.openhft.chronicle.map;
 import net.openhft.lang.Maths;
 import net.openhft.lang.collection.ATSDirectBitSet;
 import net.openhft.lang.io.DirectStore;
-import net.openhft.lang.io.NativeBytes;
+import net.openhft.lang.io.NativeBytesI;
 
 import static net.openhft.lang.Maths.isPowerOf2;
 import static net.openhft.lang.MemoryUnit.*;
@@ -39,7 +39,7 @@ enum MultiMapFactory {
         }
 
         @Override
-        public MultiMap create(NativeBytes bytes, NativeBytes bitSetBytes) {
+        public MultiMap create(NativeBytesI bytes, NativeBytesI bitSetBytes) {
             return new ShortShortMultiMap(bytes, bitSetBytes);
         }
     },
@@ -50,7 +50,7 @@ enum MultiMapFactory {
         }
 
         @Override
-        public MultiMap create(NativeBytes bytes, NativeBytes bitSetBytes) {
+        public MultiMap create(NativeBytesI bytes, NativeBytesI bitSetBytes) {
             return new Int24Int24MultiMap(bytes, bitSetBytes);
         }
     },
@@ -61,7 +61,7 @@ enum MultiMapFactory {
         }
 
         @Override
-        public MultiMap create(NativeBytes bytes, NativeBytes bitSetBytes) {
+        public MultiMap create(NativeBytesI bytes, NativeBytesI bitSetBytes) {
             return new IntIntMultiMap(bytes, bitSetBytes);
         }
     };
@@ -104,5 +104,5 @@ enum MultiMapFactory {
 
     public abstract long sizeInBytes(long minCapacity);
 
-    public abstract MultiMap create(NativeBytes bytes, NativeBytes bitSetBytes);
+    public abstract MultiMap create(NativeBytesI bytes, NativeBytesI bitSetBytes);
 }
diff --git a/src/main/java/net/openhft/chronicle/map/ReplicatedChronicleMap.java b/src/main/java/net/openhft/chronicle/map/ReplicatedChronicleMap.java
index d57cdb644..28c67936d 100644
--- a/src/main/java/net/openhft/chronicle/map/ReplicatedChronicleMap.java
+++ b/src/main/java/net/openhft/chronicle/map/ReplicatedChronicleMap.java
@@ -30,7 +30,7 @@ import net.openhft.lang.Maths;
 import net.openhft.lang.collection.ATSDirectBitSet;
 import net.openhft.lang.io.Bytes;
 import net.openhft.lang.io.MultiStoreBytes;
-import net.openhft.lang.io.NativeBytes;
+import net.openhft.lang.io.NativeBytesI;
 import net.openhft.lang.threadlocal.ThreadLocalCopies;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
@@ -126,7 +126,7 @@ final class ReplicatedChronicleMap<K, KI, MKI extends MetaBytesInterop<K, ? supe
 
     @Override
     VanillaChronicleMap<K, KI, MKI, V, VI, MVI>.Segment createSegment(
-            NativeBytes segmentHeader, NativeBytes bytes, int index) {
+            NativeBytesI segmentHeader, NativeBytesI bytes, int index) {
         return new Segment(segmentHeader, bytes, index);
     }
 
@@ -678,7 +678,7 @@ final class ReplicatedChronicleMap<K, KI, MKI extends MetaBytesInterop<K, ? supe
 
     class Segment extends VanillaChronicleMap<K, KI, MKI, V, VI, MVI>.Segment {
 
-        Segment(NativeBytes segmentHeader, NativeBytes bytes, int index) {
+        Segment(NativeBytesI segmentHeader, NativeBytesI bytes, int index) {
             super(segmentHeader, bytes, index);
         }
 
@@ -993,7 +993,7 @@ final class ReplicatedChronicleMap<K, KI, MKI extends MetaBytesInterop<K, ? supe
          * @param identifier the unique identifier relating to this map
          * @return true if the entry should not be processed
          */
-        private boolean shouldIgnore(@NotNull final NativeBytes entry, final long timestamp,
+        private boolean shouldIgnore(@NotNull final NativeBytesI entry, final long timestamp,
                                      final byte identifier) {
             final long lastModifiedTimeStamp = entry.readLong();
 
@@ -1262,7 +1262,7 @@ final class ReplicatedChronicleMap<K, KI, MKI extends MetaBytesInterop<K, ? supe
                 hashLookup().forEach(new MultiMap.EntryConsumer() {
                     @Override
                     public void accept(long hash, long pos) {
-                        final NativeBytes entry = reuse(tmpBytes, offsetFromPos(pos));
+                        final NativeBytesI entry = reuse(tmpBytes, offsetFromPos(pos));
                         long keySize = keySizeMarshaller.readSize(entry);
                         entry.skip(keySize);
 
@@ -1335,7 +1335,7 @@ final class ReplicatedChronicleMap<K, KI, MKI extends MetaBytesInterop<K, ? supe
             Segment segment = (Segment) seg;
 
             final long offset = segment.offsetFromPos(pos);
-            final NativeBytes entry = segment.reuse(this.entry, offset);
+            final NativeBytesI entry = segment.reuse(this.entry, offset);
 
             final long keySize = keySizeMarshaller.readSize(entry);
             long keyPosition = entry.position();
@@ -1490,7 +1490,7 @@ final class ReplicatedChronicleMap<K, KI, MKI extends MetaBytesInterop<K, ? supe
                         entryCallback.onBeforeEntry();
 
                         final long segmentPos = position & posMask;
-                        final NativeBytes entry =
+                        final NativeBytesI entry =
                                 segment.reuse(tmpBytes, segment.offsetFromPos(segmentPos));
 
                         // if the entry should be ignored, we'll move the next entry
diff --git a/src/main/java/net/openhft/chronicle/map/VanillaChronicleMap.java b/src/main/java/net/openhft/chronicle/map/VanillaChronicleMap.java
index e64273f5e..f876e35d7 100755
--- a/src/main/java/net/openhft/chronicle/map/VanillaChronicleMap.java
+++ b/src/main/java/net/openhft/chronicle/map/VanillaChronicleMap.java
@@ -230,7 +230,9 @@ class VanillaChronicleMap<K, KI, MKI extends MetaBytesInterop<K, ? super KI>,
     }
 
     final long createMappedStoreAndSegments(BytesStore bytesStore) throws IOException {
-        this.ms = bytesStore;
+        // checks the the store has not been closed
+        // todo remove the CheckedBytesStore before the release
+        this.ms = new CheckedBytesStore(bytesStore);
 
         onHeaderCreated();
 
@@ -242,9 +244,9 @@ class VanillaChronicleMap<K, KI, MKI extends MetaBytesInterop<K, ? super KI>,
         long segmentSize = segmentSize();
         long headerOffset = 0;
         for (int i = 0; i < this.segments.length; i++) {
-            NativeBytes segmentHeader =
-                    (NativeBytes) segmentHeaders.bytes(headerOffset, segmentHeaderSize);
-            NativeBytes segmentData = (NativeBytes) ms.bytes(offset, segmentSize);
+            NativeBytesI segmentHeader =
+                    (NativeBytesI) segmentHeaders.bytes(headerOffset, segmentHeaderSize);
+            NativeBytesI segmentData = (NativeBytesI) ms.bytes(offset, segmentSize);
             this.segments[i] = createSegment(segmentHeader, segmentData, i);
             headerOffset += segmentHeaderSize;
             offset += segmentSize;
@@ -306,7 +308,7 @@ class VanillaChronicleMap<K, KI, MKI extends MetaBytesInterop<K, ? super KI>,
         return segmentHeaderSize;
     }
 
-    Segment createSegment(NativeBytes segmentHeader, NativeBytes bytes, int index) {
+    Segment createSegment(NativeBytesI segmentHeader, NativeBytesI bytes, int index) {
         return new Segment(segmentHeader, bytes, index);
     }
 
@@ -1411,8 +1413,8 @@ class VanillaChronicleMap<K, KI, MKI extends MetaBytesInterop<K, ? super KI>,
          */
         static final long LOCK_OFFSET = 0L; // 64-bit
         static final long SIZE_OFFSET = LOCK_OFFSET + 8L; // 32-bit
-        final NativeBytes segmentHeader;
-        final NativeBytes bytes;
+        final NativeBytesI segmentHeader;
+        final NativeBytesI bytes;
         final long entriesOffset;
         private final int index;
         private final SingleThreadedDirectBitSet freeList;
@@ -1426,7 +1428,7 @@ class VanillaChronicleMap<K, KI, MKI extends MetaBytesInterop<K, ? super KI>,
         /**
          * @param index the index of this segment held by the map
          */
-        Segment(NativeBytes segmentHeader, NativeBytes bytes, int index) {
+        Segment(NativeBytesI segmentHeader, NativeBytesI bytes, int index) {
             this.segmentHeader = segmentHeader;
             this.bytes = bytes;
             this.index = index;
@@ -1435,7 +1437,7 @@ class VanillaChronicleMap<K, KI, MKI extends MetaBytesInterop<K, ? super KI>,
             hashLookup = createMultiMap(start);
             start += CACHE_LINES.align(sizeOfMultiMap() + sizeOfMultiMapBitSet(), BYTES)
                     * multiMapsPerSegment();
-            final NativeBytes bsBytes = new NativeBytes(ms.objectSerializer(),
+            final NativeBytesI bsBytes = new NativeBytes(ms.objectSerializer(),
                     start,
                     start + MultiMapFactory.sizeOfBitSetInBytes(actualChunksPerSegment),
                     null);
@@ -1453,11 +1455,11 @@ class VanillaChronicleMap<K, KI, MKI extends MetaBytesInterop<K, ? super KI>,
         }
 
         private MultiMap createMultiMap(long start) {
-            final NativeBytes multiMapBytes =
+            final NativeBytesI multiMapBytes =
                     new NativeBytes((ObjectSerializer) null, start,
                             start = start + sizeOfMultiMap(), null);
 
-            final NativeBytes sizeOfMultiMapBitSetBytes =
+            final NativeBytesI sizeOfMultiMapBitSetBytes =
                     new NativeBytes((ObjectSerializer) null, start,
                             start + sizeOfMultiMapBitSet(), null);
 //            multiMapBytes.load();
@@ -2574,7 +2576,7 @@ class VanillaChronicleMap<K, KI, MKI extends MetaBytesInterop<K, ? super KI>,
             // of returnedEntry.getKey(), but it seems rather wasteful to workaround so rare
             // case.
             final long offset = segment.offsetFromPos(pos);
-            final NativeBytes entry = segment.reuse(this.entry, offset);
+            final NativeBytesI entry = segment.reuse(this.entry, offset);
 
             final long keySize = keySizeMarshaller.readSize(entry);
             long position = entry.position();
@@ -2583,7 +2585,7 @@ class VanillaChronicleMap<K, KI, MKI extends MetaBytesInterop<K, ? super KI>,
             removePresent(segment, pos, entry, keySize, segmentHash, true);
         }
 
-        final void removePresent(Segment segment, long pos, NativeBytes entry, long keySize,
+        final void removePresent(Segment segment, long pos, NativeBytesI entry, long keySize,
                                  long segmentHash, boolean removeFromMultiMap) {
             entry.skip(keySize);
             segment.manageReplicationBytes(entry, true, true);