diff --git a/hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/BlockCacheUtil.java b/hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/BlockCacheUtil.java
index e5bb83b7799..a3d46ed37aa 100644
--- a/hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/BlockCacheUtil.java
+++ b/hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/BlockCacheUtil.java
@@ -18,6 +18,7 @@
 package org.apache.hadoop.hbase.io.hfile;
 
 import java.io.IOException;
+import java.nio.ByteBuffer;
 import java.util.NavigableMap;
 import java.util.NavigableSet;
 import java.util.concurrent.ConcurrentSkipListMap;
@@ -26,6 +27,7 @@ import java.util.concurrent.ConcurrentSkipListSet;
 import org.apache.hadoop.hbase.classification.InterfaceAudience;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.hbase.metrics.impl.FastLongHistogram;
+import org.apache.hadoop.hbase.util.Bytes;
 import org.codehaus.jackson.JsonGenerationException;
 import org.codehaus.jackson.annotate.JsonIgnoreProperties;
 import org.codehaus.jackson.map.JsonMappingException;
@@ -171,6 +173,15 @@ public class BlockCacheUtil {
     return cbsbf;
   }
 
+  public static int compareCacheBlock(Cacheable left, Cacheable right) {
+    ByteBuffer l = ByteBuffer.allocate(left.getSerializedLength());
+    left.serialize(l);
+    ByteBuffer r = ByteBuffer.allocate(right.getSerializedLength());
+    right.serialize(r);
+    return Bytes.compareTo(l.array(), l.arrayOffset(), l.limit(),
+             r.array(), r.arrayOffset(), r.limit());
+  }
+
   /**
    * Use one of these to keep a running account of cached blocks by file.  Throw it away when done.
    * This is different than metrics in that it is stats on current state of a cache.
diff --git a/hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/LruBlockCache.java b/hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/LruBlockCache.java
index 3fbe44b0b48..69fea76d147 100644
--- a/hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/LruBlockCache.java
+++ b/hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/LruBlockCache.java
@@ -373,7 +373,7 @@ public class LruBlockCache implements ResizableBlockCache, HeapSize {
     LruCachedBlock cb = map.get(cacheKey);
     if (cb != null) {
       // compare the contents, if they are not equal, we are in big trouble
-      if (compare(buf, cb.getBuffer()) != 0) {
+      if (BlockCacheUtil.compareCacheBlock(buf, cb.getBuffer()) != 0) {
         throw new RuntimeException("Cached block contents differ, which should not have happened."
           + "cacheKey:" + cacheKey);
       }
@@ -433,15 +433,6 @@ public class LruBlockCache implements ResizableBlockCache, HeapSize {
     }
   }
 
-  private int compare(Cacheable left, Cacheable right) {
-    ByteBuffer l = ByteBuffer.allocate(left.getSerializedLength());
-    left.serialize(l);
-    ByteBuffer r = ByteBuffer.allocate(right.getSerializedLength());
-    right.serialize(r);
-    return Bytes.compareTo(l.array(), l.arrayOffset(), l.limit(),
-      r.array(), r.arrayOffset(), r.limit());
-  }
-
   /**
    * Cache the block with the specified name and buffer.
    * <p>
@@ -577,7 +568,7 @@ public class LruBlockCache implements ResizableBlockCache, HeapSize {
         boolean wait = getCurrentSize() < acceptableSize();
         boolean inMemory = block.getPriority() == BlockPriority.MEMORY;
         ((BucketCache)victimHandler).cacheBlockWithWait(block.getCacheKey(), block.getBuffer(),
-            inMemory, wait);
+            inMemory, true, wait);
       } else {
         victimHandler.cacheBlock(block.getCacheKey(), block.getBuffer());
       }
diff --git a/hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/bucket/BucketCache.java b/hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/bucket/BucketCache.java
index 6d50befc30e..b8d7453af76 100644
--- a/hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/bucket/BucketCache.java
+++ b/hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/bucket/BucketCache.java
@@ -402,7 +402,7 @@ public class BucketCache implements BlockCache, HeapSize {
   @Override
   public void cacheBlock(BlockCacheKey cacheKey, Cacheable cachedItem, boolean inMemory,
       final boolean cacheDataInL1) {
-    cacheBlockWithWait(cacheKey, cachedItem, inMemory, wait_when_cache);
+    cacheBlockWithWait(cacheKey, cachedItem, inMemory, cacheDataInL1, wait_when_cache);
   }
 
   /**
@@ -413,13 +413,26 @@ public class BucketCache implements BlockCache, HeapSize {
    * @param wait if true, blocking wait when queue is full
    */
   public void cacheBlockWithWait(BlockCacheKey cacheKey, Cacheable cachedItem, boolean inMemory,
-      boolean wait) {
+      boolean cacheDataInL1, boolean wait) {
     if (LOG.isTraceEnabled()) LOG.trace("Caching key=" + cacheKey + ", item=" + cachedItem);
     if (!cacheEnabled) {
       return;
     }
 
     if (backingMap.containsKey(cacheKey)) {
+      /*
+       * Compare already cached block only if lruBlockCache is not used to cache data blocks
+       */
+      if (!cacheDataInL1) {
+        Cacheable existingBlock = getBlock(cacheKey, false, false, false);
+        if (BlockCacheUtil.compareCacheBlock(cachedItem, existingBlock) != 0) {
+          throw new RuntimeException("Cached block contents differ, which should not have happened."
+                                    + "cacheKey:" + cacheKey);
+        }
+      }
+      String msg = "Caching an already cached block: " + cacheKey;
+      msg += ". This is harmless and can happen in rare cases (see HBASE-8547)";
+      LOG.warn(msg);
       return;
     }