diff --git a/cmd/api-headers.go b/cmd/api-headers.go
index cbabee1c9..9e510084b 100644
--- a/cmd/api-headers.go
+++ b/cmd/api-headers.go
@@ -62,8 +62,8 @@ func setObjectHeaders(w http.ResponseWriter, objInfo ObjectInfo, contentRange *h
 	w.Header().Set("Last-Modified", lastModified)
 
 	// Set Etag if available.
-	if objInfo.MD5Sum != "" {
-		w.Header().Set("ETag", "\""+objInfo.MD5Sum+"\"")
+	if objInfo.ETag != "" {
+		w.Header().Set("ETag", "\""+objInfo.ETag+"\"")
 	}
 
 	// Set all other user defined metadata.
diff --git a/cmd/api-response.go b/cmd/api-response.go
index bc95cab60..794178c2b 100644
--- a/cmd/api-response.go
+++ b/cmd/api-response.go
@@ -321,8 +321,8 @@ func generateListObjectsV1Response(bucket, prefix, marker, delimiter string, max
 		}
 		content.Key = object.Name
 		content.LastModified = object.ModTime.UTC().Format(timeFormatAMZLong)
-		if object.MD5Sum != "" {
-			content.ETag = "\"" + object.MD5Sum + "\""
+		if object.ETag != "" {
+			content.ETag = "\"" + object.ETag + "\""
 		}
 		content.Size = object.Size
 		content.StorageClass = globalMinioDefaultStorageClass
@@ -370,8 +370,8 @@ func generateListObjectsV2Response(bucket, prefix, token, startAfter, delimiter
 		}
 		content.Key = object.Name
 		content.LastModified = object.ModTime.UTC().Format(timeFormatAMZLong)
-		if object.MD5Sum != "" {
-			content.ETag = "\"" + object.MD5Sum + "\""
+		if object.ETag != "" {
+			content.ETag = "\"" + object.ETag + "\""
 		}
 		content.Size = object.Size
 		content.StorageClass = globalMinioDefaultStorageClass
diff --git a/cmd/benchmark-utils_test.go b/cmd/benchmark-utils_test.go
index ca1c4dc41..f871c844a 100644
--- a/cmd/benchmark-utils_test.go
+++ b/cmd/benchmark-utils_test.go
@@ -49,7 +49,7 @@ func runPutObjectBenchmark(b *testing.B, obj ObjectLayer, objSize int) {
 	// generate md5sum for the generated data.
 	// md5sum of the data to written is required as input for PutObject.
 	metadata := make(map[string]string)
-	metadata["md5Sum"] = getMD5Hash(textData)
+	metadata["etag"] = getMD5Hash(textData)
 	sha256sum := ""
 	// benchmark utility which helps obtain number of allocations and bytes allocated per ops.
 	b.ReportAllocs()
@@ -61,8 +61,8 @@ func runPutObjectBenchmark(b *testing.B, obj ObjectLayer, objSize int) {
 		if err != nil {
 			b.Fatal(err)
 		}
-		if objInfo.MD5Sum != metadata["md5Sum"] {
-			b.Fatalf("Write no: %d: Md5Sum mismatch during object write into the bucket: Expected %s, got %s", i+1, objInfo.MD5Sum, metadata["md5Sum"])
+		if objInfo.ETag != metadata["etag"] {
+			b.Fatalf("Write no: %d: Md5Sum mismatch during object write into the bucket: Expected %s, got %s", i+1, objInfo.ETag, metadata["etag"])
 		}
 	}
 	// Benchmark ends here. Stop timer.
@@ -85,15 +85,15 @@ func runPutObjectPartBenchmark(b *testing.B, obj ObjectLayer, partSize int) {
 
 	objSize := 128 * humanize.MiByte
 
-	// PutObjectPart returns md5Sum of the object inserted.
-	// md5Sum variable is assigned with that value.
-	var md5Sum, uploadID string
+	// PutObjectPart returns etag of the object inserted.
+	// etag variable is assigned with that value.
+	var etag, uploadID string
 	// get text data generated for number of bytes equal to object size.
 	textData := generateBytesData(objSize)
 	// generate md5sum for the generated data.
 	// md5sum of the data to written is required as input for NewMultipartUpload.
 	metadata := make(map[string]string)
-	metadata["md5Sum"] = getMD5Hash(textData)
+	metadata["etag"] = getMD5Hash(textData)
 	sha256sum := ""
 	uploadID, err = obj.NewMultipartUpload(bucket, object, metadata)
 	if err != nil {
@@ -115,14 +115,14 @@ func runPutObjectPartBenchmark(b *testing.B, obj ObjectLayer, partSize int) {
 				textPartData = textData[j*partSize:]
 			}
 			metadata := make(map[string]string)
-			metadata["md5Sum"] = getMD5Hash([]byte(textPartData))
+			metadata["etag"] = getMD5Hash([]byte(textPartData))
 			var partInfo PartInfo
-			partInfo, err = obj.PutObjectPart(bucket, object, uploadID, j, int64(len(textPartData)), bytes.NewBuffer(textPartData), metadata["md5Sum"], sha256sum)
+			partInfo, err = obj.PutObjectPart(bucket, object, uploadID, j, int64(len(textPartData)), bytes.NewBuffer(textPartData), metadata["etag"], sha256sum)
 			if err != nil {
 				b.Fatal(err)
 			}
-			if partInfo.ETag != metadata["md5Sum"] {
-				b.Fatalf("Write no: %d: Md5Sum mismatch during object write into the bucket: Expected %s, got %s", i+1, md5Sum, metadata["md5Sum"])
+			if partInfo.ETag != metadata["etag"] {
+				b.Fatalf("Write no: %d: Md5Sum mismatch during object write into the bucket: Expected %s, got %s", i+1, etag, metadata["etag"])
 			}
 		}
 	}
@@ -208,19 +208,19 @@ func runGetObjectBenchmark(b *testing.B, obj ObjectLayer, objSize int) {
 	for i := 0; i < 10; i++ {
 		// get text data generated for number of bytes equal to object size.
 		textData := generateBytesData(objSize)
-		// generate md5sum for the generated data.
-		// md5sum of the data to written is required as input for PutObject.
+		// generate etag for the generated data.
+		// etag of the data to written is required as input for PutObject.
 		// PutObject is the functions which writes the data onto the FS/XL backend.
 		metadata := make(map[string]string)
-		metadata["md5Sum"] = getMD5Hash(textData)
+		metadata["etag"] = getMD5Hash(textData)
 		// insert the object.
 		var objInfo ObjectInfo
 		objInfo, err = obj.PutObject(bucket, "object"+strconv.Itoa(i), int64(len(textData)), bytes.NewBuffer(textData), metadata, sha256sum)
 		if err != nil {
 			b.Fatal(err)
 		}
-		if objInfo.MD5Sum != metadata["md5Sum"] {
-			b.Fatalf("Write no: %d: Md5Sum mismatch during object write into the bucket: Expected %s, got %s", i+1, objInfo.MD5Sum, metadata["md5Sum"])
+		if objInfo.ETag != metadata["etag"] {
+			b.Fatalf("Write no: %d: Md5Sum mismatch during object write into the bucket: Expected %s, got %s", i+1, objInfo.ETag, metadata["etag"])
 		}
 	}
 
@@ -317,7 +317,7 @@ func runPutObjectBenchmarkParallel(b *testing.B, obj ObjectLayer, objSize int) {
 	// generate md5sum for the generated data.
 	// md5sum of the data to written is required as input for PutObject.
 	metadata := make(map[string]string)
-	metadata["md5Sum"] = getMD5Hash([]byte(textData))
+	metadata["etag"] = getMD5Hash([]byte(textData))
 	sha256sum := ""
 	// benchmark utility which helps obtain number of allocations and bytes allocated per ops.
 	b.ReportAllocs()
@@ -332,8 +332,8 @@ func runPutObjectBenchmarkParallel(b *testing.B, obj ObjectLayer, objSize int) {
 			if err != nil {
 				b.Fatal(err)
 			}
-			if objInfo.MD5Sum != metadata["md5Sum"] {
-				b.Fatalf("Write no: Md5Sum mismatch during object write into the bucket: Expected %s, got %s", objInfo.MD5Sum, metadata["md5Sum"])
+			if objInfo.ETag != metadata["etag"] {
+				b.Fatalf("Write no: Md5Sum mismatch during object write into the bucket: Expected %s, got %s", objInfo.ETag, metadata["etag"])
 			}
 			i++
 		}
@@ -367,7 +367,7 @@ func runGetObjectBenchmarkParallel(b *testing.B, obj ObjectLayer, objSize int) {
 		// md5sum of the data to written is required as input for PutObject.
 		// PutObject is the functions which writes the data onto the FS/XL backend.
 		metadata := make(map[string]string)
-		metadata["md5Sum"] = getMD5Hash([]byte(textData))
+		metadata["etag"] = getMD5Hash([]byte(textData))
 		sha256sum := ""
 		// insert the object.
 		var objInfo ObjectInfo
@@ -375,8 +375,8 @@ func runGetObjectBenchmarkParallel(b *testing.B, obj ObjectLayer, objSize int) {
 		if err != nil {
 			b.Fatal(err)
 		}
-		if objInfo.MD5Sum != metadata["md5Sum"] {
-			b.Fatalf("Write no: %d: Md5Sum mismatch during object write into the bucket: Expected %s, got %s", i+1, objInfo.MD5Sum, metadata["md5Sum"])
+		if objInfo.ETag != metadata["etag"] {
+			b.Fatalf("Write no: %d: Md5Sum mismatch during object write into the bucket: Expected %s, got %s", i+1, objInfo.ETag, metadata["etag"])
 		}
 	}
 
diff --git a/cmd/bucket-handlers.go b/cmd/bucket-handlers.go
index 91b67c4a9..c997c1dba 100644
--- a/cmd/bucket-handlers.go
+++ b/cmd/bucket-handlers.go
@@ -535,7 +535,7 @@ func (api objectAPIHandlers) PostPolicyBucketHandler(w http.ResponseWriter, r *h
 		return
 	}
 
-	w.Header().Set("ETag", `"`+objInfo.MD5Sum+`"`)
+	w.Header().Set("ETag", `"`+objInfo.ETag+`"`)
 	w.Header().Set("Location", getObjectLocation(bucket, object))
 
 	// Get host and port from Request.RemoteAddr.
@@ -568,7 +568,7 @@ func (api objectAPIHandlers) PostPolicyBucketHandler(w http.ResponseWriter, r *h
 		resp := encodeResponse(PostResponse{
 			Bucket:   objInfo.Bucket,
 			Key:      objInfo.Name,
-			ETag:     `"` + objInfo.MD5Sum + `"`,
+			ETag:     `"` + objInfo.ETag + `"`,
 			Location: getObjectLocation(objInfo.Bucket, objInfo.Name),
 		})
 		writeResponse(w, http.StatusCreated, resp, "application/xml")
diff --git a/cmd/event-notifier.go b/cmd/event-notifier.go
index e8d012348..9e5003973 100644
--- a/cmd/event-notifier.go
+++ b/cmd/event-notifier.go
@@ -172,7 +172,7 @@ func newNotificationEvent(event eventData) NotificationEvent {
 	// For all other events we should set ETag and Size.
 	nEvent.S3.Object = objectMeta{
 		Key:         escapedObj,
-		ETag:        event.ObjInfo.MD5Sum,
+		ETag:        event.ObjInfo.ETag,
 		Size:        event.ObjInfo.Size,
 		ContentType: event.ObjInfo.ContentType,
 		UserDefined: event.ObjInfo.UserDefined,
diff --git a/cmd/fs-v1-metadata.go b/cmd/fs-v1-metadata.go
index 4df6a8516..fdbc4eaf4 100644
--- a/cmd/fs-v1-metadata.go
+++ b/cmd/fs-v1-metadata.go
@@ -33,11 +33,31 @@ import (
 	"github.com/tidwall/gjson"
 )
 
+// FS format, and object metadata.
 const (
-	fsMetaJSONFile   = "fs.json"
+	// fs.json object metadata.
+	fsMetaJSONFile = "fs.json"
+	// format.json FS format metadata.
 	fsFormatJSONFile = "format.json"
 )
 
+// FS metadata constants.
+const (
+	// FS backend meta 1.0.0 version.
+	fsMetaVersion100 = "1.0.0"
+
+	// FS backend meta 1.0.1 version.
+	fsMetaVersion = "1.0.1"
+
+	// FS backend meta format.
+	fsMetaFormat = "fs"
+
+	// FS backend format version.
+	fsFormatVersion = fsFormatV2
+
+	// Add more constants here.
+)
+
 // A fsMetaV1 represents a metadata header mapping keys to sets of values.
 type fsMetaV1 struct {
 	Version string `json:"version"`
@@ -50,6 +70,19 @@ type fsMetaV1 struct {
 	Parts []objectPartInfo  `json:"parts,omitempty"`
 }
 
+// IsValid - tells if the format is sane by validating the version
+// string and format style.
+func (m fsMetaV1) IsValid() bool {
+	return isFSMetaValid(m.Version, m.Format)
+}
+
+// Verifies if the backend format metadata is sane by validating
+// the version string and format style.
+func isFSMetaValid(version, format string) bool {
+	return ((version == fsMetaVersion || version == fsMetaVersion100) &&
+		format == fsMetaFormat)
+}
+
 // Converts metadata to object info.
 func (m fsMetaV1) ToObjectInfo(bucket, object string, fi os.FileInfo) ObjectInfo {
 	if len(m.Meta) == 0 {
@@ -78,17 +111,15 @@ func (m fsMetaV1) ToObjectInfo(bucket, object string, fi os.FileInfo) ObjectInfo
 		objInfo.IsDir = fi.IsDir()
 	}
 
-	objInfo.MD5Sum = m.Meta["md5Sum"]
+	// Extract etag from metadata.
+	objInfo.ETag = extractETag(m.Meta)
 	objInfo.ContentType = m.Meta["content-type"]
 	objInfo.ContentEncoding = m.Meta["content-encoding"]
 
-	// md5Sum has already been extracted into objInfo.MD5Sum.  We
-	// need to remove it from m.Meta to avoid it from appearing as
-	// part of response headers. e.g, X-Minio-* or X-Amz-*.
-	delete(m.Meta, "md5Sum")
-
-	// Save all the other userdefined API.
-	objInfo.UserDefined = m.Meta
+	// etag/md5Sum has already been extracted. We need to
+	// remove to avoid it from appearing as part of
+	// response headers. e.g, X-Minio-* or X-Amz-*.
+	objInfo.UserDefined = cleanMetaETag(m.Meta)
 
 	// Success..
 	return objInfo
@@ -207,6 +238,12 @@ func (m *fsMetaV1) ReadFrom(lk *lock.LockedFile) (n int64, err error) {
 	// obtain format.
 	m.Format = parseFSFormat(fsMetaBuf)
 
+	// Verify if the format is valid, return corrupted format
+	// for unrecognized formats.
+	if !isFSMetaValid(m.Version, m.Format) {
+		return 0, traceError(errCorruptedFormat)
+	}
+
 	// obtain metadata.
 	m.Meta = parseFSMetaMap(fsMetaBuf)
 
@@ -220,20 +257,6 @@ func (m *fsMetaV1) ReadFrom(lk *lock.LockedFile) (n int64, err error) {
 	return int64(len(fsMetaBuf)), nil
 }
 
-// FS metadata constants.
-const (
-	// FS backend meta version.
-	fsMetaVersion = "1.0.0"
-
-	// FS backend meta format.
-	fsMetaFormat = "fs"
-
-	// FS backend format version.
-	fsFormatVersion = fsFormatV2
-
-	// Add more constants here.
-)
-
 // FS format version strings.
 const (
 	fsFormatV1 = "1" // Previous format.
diff --git a/cmd/fs-v1-metadata_test.go b/cmd/fs-v1-metadata_test.go
index 620c43b5c..9d960f067 100644
--- a/cmd/fs-v1-metadata_test.go
+++ b/cmd/fs-v1-metadata_test.go
@@ -110,10 +110,10 @@ func TestWriteFSMetadata(t *testing.T) {
 	if err != nil {
 		t.Fatal("Unexpected error ", err)
 	}
-	if fsMeta.Version != "1.0.0" {
+	if fsMeta.Version != fsMetaVersion {
 		t.Fatalf("Unexpected version %s", fsMeta.Version)
 	}
-	if fsMeta.Format != "fs" {
+	if fsMeta.Format != fsMetaFormat {
 		t.Fatalf("Unexpected format %s", fsMeta.Format)
 	}
 }
diff --git a/cmd/fs-v1-multipart.go b/cmd/fs-v1-multipart.go
index 14c3c1c12..4410fb75a 100644
--- a/cmd/fs-v1-multipart.go
+++ b/cmd/fs-v1-multipart.go
@@ -871,7 +871,7 @@ func (fs fsObjects) CompleteMultipartUpload(bucket string, object string, upload
 	if len(fsMeta.Meta) == 0 {
 		fsMeta.Meta = make(map[string]string)
 	}
-	fsMeta.Meta["md5Sum"] = s3MD5
+	fsMeta.Meta["etag"] = s3MD5
 
 	// Write all the set metadata.
 	if _, err = fsMeta.WriteTo(metaFile); err != nil {
diff --git a/cmd/fs-v1.go b/cmd/fs-v1.go
index 5d6c64bde..4f862285a 100644
--- a/cmd/fs-v1.go
+++ b/cmd/fs-v1.go
@@ -712,12 +712,12 @@ func (fs fsObjects) PutObject(bucket string, object string, size int64, data io.
 
 	newMD5Hex := hex.EncodeToString(md5Writer.Sum(nil))
 	// Update the md5sum if not set with the newly calculated one.
-	if len(metadata["md5Sum"]) == 0 {
-		metadata["md5Sum"] = newMD5Hex
+	if len(metadata["etag"]) == 0 {
+		metadata["etag"] = newMD5Hex
 	}
 
 	// md5Hex representation.
-	md5Hex := metadata["md5Sum"]
+	md5Hex := metadata["etag"]
 	if md5Hex != "" {
 		if newMD5Hex != md5Hex {
 			// Returns md5 mismatch.
@@ -849,8 +849,12 @@ func (fs fsObjects) getObjectETag(bucket, entry string) (string, error) {
 		}
 	}
 
-	fsMetaMap := parseFSMetaMap(fsMetaBuf)
-	return fsMetaMap["md5Sum"], nil
+	// Check if FS metadata is valid, if not return error.
+	if !isFSMetaValid(parseFSVersion(fsMetaBuf), parseFSFormat(fsMetaBuf)) {
+		return "", toObjectErr(traceError(errCorruptedFormat), bucket, entry)
+	}
+
+	return extractETag(parseFSMetaMap(fsMetaBuf)), nil
 }
 
 // ListObjects - list all objects at prefix upto maxKeys., optionally delimited by '/'. Maintains the list pool
@@ -901,8 +905,8 @@ func (fs fsObjects) ListObjects(bucket, prefix, marker, delimiter string, maxKey
 		// Protect reading `fs.json`.
 		objectLock := globalNSMutex.NewNSLock(bucket, entry)
 		objectLock.RLock()
-		var md5Sum string
-		md5Sum, err = fs.getObjectETag(bucket, entry)
+		var etag string
+		etag, err = fs.getObjectETag(bucket, entry)
 		objectLock.RUnlock()
 		if err != nil {
 			return ObjectInfo{}, err
@@ -922,7 +926,7 @@ func (fs fsObjects) ListObjects(bucket, prefix, marker, delimiter string, maxKey
 			Size:    fi.Size(),
 			ModTime: fi.ModTime(),
 			IsDir:   fi.IsDir(),
-			MD5Sum:  md5Sum,
+			ETag:    etag,
 		}, nil
 	}
 
diff --git a/cmd/fs-v1_test.go b/cmd/fs-v1_test.go
index 11c4dc313..a425ba3e4 100644
--- a/cmd/fs-v1_test.go
+++ b/cmd/fs-v1_test.go
@@ -244,7 +244,7 @@ func TestFSMigrateObjectWithObjects(t *testing.T) {
 	fsPath1 := pathJoin(bucketMetaPrefix, "testvolume1", "my-object1", fsMetaJSONFile)
 	fsPath1 = pathJoin(disk, minioMetaBucket, fsPath1)
 
-	fsMetaJSON := `{"version":"1.0.0","format":"fs","minio":{"release":"DEVELOPMENT.2017-03-27T02-26-33Z"},"meta":{"md5Sum":"467886be95c8ecfd71a2900e3f461b4f"}`
+	fsMetaJSON := `{"version":"1.0.0","format":"fs","minio":{"release":"DEVELOPMENT.2017-03-27T02-26-33Z"},"meta":{"etag":"467886be95c8ecfd71a2900e3f461b4f"}`
 	if _, err = fsCreateFile(fsPath1, bytes.NewReader([]byte(fsMetaJSON)), nil, 0); err != nil {
 		t.Fatal(err)
 	}
@@ -253,7 +253,7 @@ func TestFSMigrateObjectWithObjects(t *testing.T) {
 	fsPath2 := pathJoin(bucketMetaPrefix, "testvolume2", "my-object2", fsMetaJSONFile)
 	fsPath2 = pathJoin(disk, minioMetaBucket, fsPath2)
 
-	fsMetaJSON = `{"version":"1.0.0","format":"fs","minio":{"release":"DEVELOPMENT.2017-03-27T02-26-33Z"},"meta":{"md5Sum":"467886be95c8ecfd71a2900eff461b4d"}`
+	fsMetaJSON = `{"version":"1.0.0","format":"fs","minio":{"release":"DEVELOPMENT.2017-03-27T02-26-33Z"},"meta":{"etag":"467886be95c8ecfd71a2900eff461b4d"}`
 	if _, err = fsCreateFile(fsPath2, bytes.NewReader([]byte(fsMetaJSON)), nil, 0); err != nil {
 		t.Fatal(err)
 	}
diff --git a/cmd/gateway-azure-anonymous.go b/cmd/gateway-azure-anonymous.go
index 69dcc1aa5..48b936343 100644
--- a/cmd/gateway-azure-anonymous.go
+++ b/cmd/gateway-azure-anonymous.go
@@ -127,7 +127,7 @@ func (a AzureObjects) AnonGetObjectInfo(bucket, object string) (objInfo ObjectIn
 		objInfo.UserDefined["Content-Encoding"] = resp.Header.Get("Content-Encoding")
 	}
 	objInfo.UserDefined["Content-Type"] = resp.Header.Get("Content-Type")
-	objInfo.MD5Sum = resp.Header.Get("Etag")
+	objInfo.ETag = resp.Header.Get("Etag")
 	objInfo.ModTime = t
 	objInfo.Name = object
 	objInfo.Size = contentLength
@@ -182,7 +182,7 @@ func (a AzureObjects) AnonListObjects(bucket, prefix, marker, delimiter string,
 			Name:            object.Name,
 			ModTime:         t,
 			Size:            object.Properties.ContentLength,
-			MD5Sum:          object.Properties.Etag,
+			ETag:            object.Properties.Etag,
 			ContentType:     object.Properties.ContentType,
 			ContentEncoding: object.Properties.ContentEncoding,
 		})
diff --git a/cmd/gateway-azure.go b/cmd/gateway-azure.go
index da9b74630..22082b11c 100644
--- a/cmd/gateway-azure.go
+++ b/cmd/gateway-azure.go
@@ -235,7 +235,7 @@ func (a AzureObjects) ListObjects(bucket, prefix, marker, delimiter string, maxK
 			Name:            object.Name,
 			ModTime:         t,
 			Size:            object.Properties.ContentLength,
-			MD5Sum:          canonicalizeETag(object.Properties.Etag),
+			ETag:            canonicalizeETag(object.Properties.Etag),
 			ContentType:     object.Properties.ContentType,
 			ContentEncoding: object.Properties.ContentEncoding,
 		})
@@ -285,7 +285,7 @@ func (a AzureObjects) GetObjectInfo(bucket, object string) (objInfo ObjectInfo,
 	objInfo = ObjectInfo{
 		Bucket:      bucket,
 		UserDefined: make(map[string]string),
-		MD5Sum:      canonicalizeETag(prop.Etag),
+		ETag:        canonicalizeETag(prop.Etag),
 		ModTime:     t,
 		Name:        object,
 		Size:        prop.ContentLength,
@@ -319,7 +319,7 @@ func (a AzureObjects) PutObject(bucket, object string, size int64, data io.Reade
 		teeReader = io.TeeReader(data, sha256Writer)
 	}
 
-	delete(metadata, "md5Sum")
+	delete(metadata, "etag")
 
 	err = a.client.CreateBlockBlobFromReader(bucket, object, uint64(size), teeReader, canonicalMetadata(metadata))
 	if err != nil {
diff --git a/cmd/gateway-handlers.go b/cmd/gateway-handlers.go
index bce48a8dd..456b4446d 100644
--- a/cmd/gateway-handlers.go
+++ b/cmd/gateway-handlers.go
@@ -234,7 +234,7 @@ func (api gatewayAPIHandlers) PutObjectHandler(w http.ResponseWriter, r *http.Re
 	}
 
 	// Make sure we hex encode md5sum here.
-	metadata["md5Sum"] = hex.EncodeToString(md5Bytes)
+	metadata["etag"] = hex.EncodeToString(md5Bytes)
 
 	sha256sum := ""
 
@@ -282,7 +282,7 @@ func (api gatewayAPIHandlers) PutObjectHandler(w http.ResponseWriter, r *http.Re
 		return
 	}
 
-	w.Header().Set("ETag", "\""+objInfo.MD5Sum+"\"")
+	w.Header().Set("ETag", "\""+objInfo.ETag+"\"")
 	writeSuccessResponseHeadersOnly(w)
 }
 
diff --git a/cmd/gateway-s3-anonymous.go b/cmd/gateway-s3-anonymous.go
index d4fc4e31a..4fbb1b716 100644
--- a/cmd/gateway-s3-anonymous.go
+++ b/cmd/gateway-s3-anonymous.go
@@ -36,13 +36,13 @@ func (l *s3Gateway) AnonPutObject(bucket string, object string, size int64, data
 	}
 
 	var md5sumBytes []byte
-	md5sum := metadata["md5Sum"]
+	md5sum := metadata["etag"]
 	if md5sum != "" {
 		md5sumBytes, err = hex.DecodeString(md5sum)
 		if err != nil {
 			return ObjectInfo{}, s3ToObjectError(traceError(err), bucket, object)
 		}
-		delete(metadata, "md5Sum")
+		delete(metadata, "etag")
 	}
 
 	oi, err := l.anonClient.PutObject(bucket, object, size, data, md5sumBytes, sha256sumBytes, toMinioClientMetadata(metadata))
diff --git a/cmd/gateway-s3.go b/cmd/gateway-s3.go
index f2be3f269..2a09d5fc7 100644
--- a/cmd/gateway-s3.go
+++ b/cmd/gateway-s3.go
@@ -295,7 +295,7 @@ func fromMinioClientObjectInfo(bucket string, oi minio.ObjectInfo) ObjectInfo {
 		Name:            oi.Key,
 		ModTime:         oi.LastModified,
 		Size:            oi.Size,
-		MD5Sum:          oi.ETag,
+		ETag:            oi.ETag,
 		UserDefined:     userDefined,
 		ContentType:     oi.ContentType,
 		ContentEncoding: oi.Metadata.Get("Content-Encoding"),
@@ -326,13 +326,13 @@ func (l *s3Gateway) PutObject(bucket string, object string, size int64, data io.
 	}
 
 	var md5sumBytes []byte
-	md5sum := metadata["md5Sum"]
+	md5sum := metadata["etag"]
 	if md5sum != "" {
 		md5sumBytes, err = hex.DecodeString(md5sum)
 		if err != nil {
 			return ObjectInfo{}, s3ToObjectError(traceError(err), bucket, object)
 		}
-		delete(metadata, "md5Sum")
+		delete(metadata, "etag")
 	}
 
 	oi, err := l.Client.PutObject(bucket, object, size, data, md5sumBytes, sha256sumBytes, toMinioClientMetadata(metadata))
diff --git a/cmd/handler-utils.go b/cmd/handler-utils.go
index e6c9dc35b..46b1d4158 100644
--- a/cmd/handler-utils.go
+++ b/cmd/handler-utils.go
@@ -134,7 +134,7 @@ func getRedirectPostRawQuery(objInfo ObjectInfo) string {
 	redirectValues := make(url.Values)
 	redirectValues.Set("bucket", objInfo.Bucket)
 	redirectValues.Set("key", objInfo.Name)
-	redirectValues.Set("etag", "\""+objInfo.MD5Sum+"\"")
+	redirectValues.Set("etag", "\""+objInfo.ETag+"\"")
 	return redirectValues.Encode()
 }
 
diff --git a/cmd/object-api-common.go b/cmd/object-api-common.go
index b2056f01d..506a91ec7 100644
--- a/cmd/object-api-common.go
+++ b/cmd/object-api-common.go
@@ -35,8 +35,8 @@ const (
 	// Objects meta prefix.
 	objectMetaPrefix = "objects"
 
-	// Md5Sum of empty string.
-	emptyStrMd5Sum = "d41d8cd98f00b204e9800998ecf8427e"
+	// ETag (hex encoded md5sum) of empty string.
+	emptyETag = "d41d8cd98f00b204e9800998ecf8427e"
 )
 
 // Global object layer mutex, used for safely updating object layer.
@@ -68,10 +68,10 @@ func dirObjectInfo(bucket, object string, size int64, metadata map[string]string
 	// This is a special case with size as '0' and object ends with
 	// a slash separator, we treat it like a valid operation and
 	// return success.
-	md5Sum := metadata["md5Sum"]
-	delete(metadata, "md5Sum")
-	if md5Sum == "" {
-		md5Sum = emptyStrMd5Sum
+	etag := metadata["etag"]
+	delete(metadata, "etag")
+	if etag == "" {
+		etag = emptyETag
 	}
 
 	return ObjectInfo{
@@ -81,7 +81,7 @@ func dirObjectInfo(bucket, object string, size int64, metadata map[string]string
 		ContentType: "application/octet-stream",
 		IsDir:       true,
 		Size:        size,
-		MD5Sum:      md5Sum,
+		ETag:        etag,
 		UserDefined: metadata,
 	}
 }
diff --git a/cmd/object-api-datatypes.go b/cmd/object-api-datatypes.go
index 4561b82bd..7ebc1644c 100644
--- a/cmd/object-api-datatypes.go
+++ b/cmd/object-api-datatypes.go
@@ -101,8 +101,8 @@ type ObjectInfo struct {
 	// IsDir indicates if the object is prefix.
 	IsDir bool
 
-	// Hex encoded md5 checksum of the object.
-	MD5Sum string
+	// Hex encoded unique entity tag of the object.
+	ETag string
 
 	// A standard MIME type describing the format of the object.
 	ContentType string
diff --git a/cmd/object-api-listobjects_test.go b/cmd/object-api-listobjects_test.go
index 9d469f766..560a36101 100644
--- a/cmd/object-api-listobjects_test.go
+++ b/cmd/object-api-listobjects_test.go
@@ -549,7 +549,7 @@ func testListObjects(obj ObjectLayer, instanceType string, t TestErrHandler) {
 				if testCase.result.Objects[j].Name != result.Objects[j].Name {
 					t.Errorf("Test %d: %s: Expected object name to be \"%s\", but found \"%s\" instead", i+1, instanceType, testCase.result.Objects[j].Name, result.Objects[j].Name)
 				}
-				if result.Objects[j].MD5Sum == "" {
+				if result.Objects[j].ETag == "" {
 					t.Errorf("Test %d: %s: Expected md5sum to be not empty, but found empty instead", i+1, instanceType)
 				}
 
diff --git a/cmd/object-api-multipart_test.go b/cmd/object-api-multipart_test.go
index b78bb8c7d..263bb36ae 100644
--- a/cmd/object-api-multipart_test.go
+++ b/cmd/object-api-multipart_test.go
@@ -1930,7 +1930,7 @@ func testObjectCompleteMultipartUpload(obj ObjectLayer, instanceType string, t T
 		if actualErr == nil && testCase.shouldPass {
 
 			// Asserting IsTruncated.
-			if actualResult.MD5Sum != testCase.expectedS3MD5 {
+			if actualResult.ETag != testCase.expectedS3MD5 {
 				t.Errorf("Test %d: %s: Expected the result to be \"%v\", but found it to \"%v\"", i+1, instanceType, testCase.expectedS3MD5, actualResult)
 			}
 		}
diff --git a/cmd/object-api-putobject_test.go b/cmd/object-api-putobject_test.go
index 3e889bfb9..4a8e702ce 100644
--- a/cmd/object-api-putobject_test.go
+++ b/cmd/object-api-putobject_test.go
@@ -29,7 +29,7 @@ import (
 )
 
 func md5Header(data []byte) map[string]string {
-	return map[string]string{"md5Sum": getMD5Hash([]byte(data))}
+	return map[string]string{"etag": getMD5Hash([]byte(data))}
 }
 
 // Wrapper for calling PutObject tests for both XL multiple disks and single node setup.
@@ -94,29 +94,29 @@ func testObjectAPIPutObject(obj ObjectLayer, instanceType string, t TestErrHandl
 
 		// Test case - 7.
 		// Input to replicate Md5 mismatch.
-		{bucket, object, []byte(""), map[string]string{"md5Sum": "a35"}, "", 0, "",
+		{bucket, object, []byte(""), map[string]string{"etag": "a35"}, "", 0, "",
 			BadDigest{ExpectedMD5: "a35", CalculatedMD5: "d41d8cd98f00b204e9800998ecf8427e"}},
 
 		// Test case - 8.
 		// With incorrect sha256.
-		{bucket, object, []byte("abcd"), map[string]string{"md5Sum": "e2fc714c4727ee9395f324cd2e7f331f"}, "incorrect-sha256", int64(len("abcd")), "", SHA256Mismatch{}},
+		{bucket, object, []byte("abcd"), map[string]string{"etag": "e2fc714c4727ee9395f324cd2e7f331f"}, "incorrect-sha256", int64(len("abcd")), "", SHA256Mismatch{}},
 
 		// Test case - 9.
 		// Input with size more than the size of actual data inside the reader.
-		{bucket, object, []byte("abcd"), map[string]string{"md5Sum": "a35"}, "", int64(len("abcd") + 1), "",
+		{bucket, object, []byte("abcd"), map[string]string{"etag": "a35"}, "", int64(len("abcd") + 1), "",
 			IncompleteBody{}},
 
 		// Test case - 10.
 		// Input with size less than the size of actual data inside the reader.
-		{bucket, object, []byte("abcd"), map[string]string{"md5Sum": "a35"}, "", int64(len("abcd") - 1), "",
+		{bucket, object, []byte("abcd"), map[string]string{"etag": "a35"}, "", int64(len("abcd") - 1), "",
 			BadDigest{ExpectedMD5: "a35", CalculatedMD5: "900150983cd24fb0d6963f7d28e17f72"}},
 
 		// Test case - 11-14.
 		// Validating for success cases.
-		{bucket, object, []byte("abcd"), map[string]string{"md5Sum": "e2fc714c4727ee9395f324cd2e7f331f"}, "", int64(len("abcd")), "", nil},
-		{bucket, object, []byte("efgh"), map[string]string{"md5Sum": "1f7690ebdd9b4caf8fab49ca1757bf27"}, "", int64(len("efgh")), "", nil},
-		{bucket, object, []byte("ijkl"), map[string]string{"md5Sum": "09a0877d04abf8759f99adec02baf579"}, "", int64(len("ijkl")), "", nil},
-		{bucket, object, []byte("mnop"), map[string]string{"md5Sum": "e132e96a5ddad6da8b07bba6f6131fef"}, "", int64(len("mnop")), "", nil},
+		{bucket, object, []byte("abcd"), map[string]string{"etag": "e2fc714c4727ee9395f324cd2e7f331f"}, "", int64(len("abcd")), "", nil},
+		{bucket, object, []byte("efgh"), map[string]string{"etag": "1f7690ebdd9b4caf8fab49ca1757bf27"}, "", int64(len("efgh")), "", nil},
+		{bucket, object, []byte("ijkl"), map[string]string{"etag": "09a0877d04abf8759f99adec02baf579"}, "", int64(len("ijkl")), "", nil},
+		{bucket, object, []byte("mnop"), map[string]string{"etag": "e132e96a5ddad6da8b07bba6f6131fef"}, "", int64(len("mnop")), "", nil},
 
 		// Test case 15-17.
 		// With no metadata
@@ -169,8 +169,8 @@ func testObjectAPIPutObject(obj ObjectLayer, instanceType string, t TestErrHandl
 		// Test passes as expected, but the output values are verified for correctness here.
 		if actualErr == nil {
 			// Asserting whether the md5 output is correct.
-			if expectedMD5, ok := testCase.inputMeta["md5Sum"]; ok && expectedMD5 != objInfo.MD5Sum {
-				t.Errorf("Test %d: %s: Calculated Md5 different from the actual one %s.", i+1, instanceType, objInfo.MD5Sum)
+			if expectedMD5, ok := testCase.inputMeta["etag"]; ok && expectedMD5 != objInfo.ETag {
+				t.Errorf("Test %d: %s: Calculated Md5 different from the actual one %s.", i+1, instanceType, objInfo.ETag)
 			}
 		}
 	}
@@ -220,10 +220,10 @@ func testObjectAPIPutObjectDiskNotFound(obj ObjectLayer, instanceType string, di
 		expectedError error
 	}{
 		// Validating for success cases.
-		{bucket, object, []byte("abcd"), map[string]string{"md5Sum": "e2fc714c4727ee9395f324cd2e7f331f"}, int64(len("abcd")), true, "", nil},
-		{bucket, object, []byte("efgh"), map[string]string{"md5Sum": "1f7690ebdd9b4caf8fab49ca1757bf27"}, int64(len("efgh")), true, "", nil},
-		{bucket, object, []byte("ijkl"), map[string]string{"md5Sum": "09a0877d04abf8759f99adec02baf579"}, int64(len("ijkl")), true, "", nil},
-		{bucket, object, []byte("mnop"), map[string]string{"md5Sum": "e132e96a5ddad6da8b07bba6f6131fef"}, int64(len("mnop")), true, "", nil},
+		{bucket, object, []byte("abcd"), map[string]string{"etag": "e2fc714c4727ee9395f324cd2e7f331f"}, int64(len("abcd")), true, "", nil},
+		{bucket, object, []byte("efgh"), map[string]string{"etag": "1f7690ebdd9b4caf8fab49ca1757bf27"}, int64(len("efgh")), true, "", nil},
+		{bucket, object, []byte("ijkl"), map[string]string{"etag": "09a0877d04abf8759f99adec02baf579"}, int64(len("ijkl")), true, "", nil},
+		{bucket, object, []byte("mnop"), map[string]string{"etag": "e132e96a5ddad6da8b07bba6f6131fef"}, int64(len("mnop")), true, "", nil},
 	}
 
 	sha256sum := ""
@@ -246,8 +246,8 @@ func testObjectAPIPutObjectDiskNotFound(obj ObjectLayer, instanceType string, di
 		// Test passes as expected, but the output values are verified for correctness here.
 		if actualErr == nil && testCase.shouldPass {
 			// Asserting whether the md5 output is correct.
-			if testCase.inputMeta["md5Sum"] != objInfo.MD5Sum {
-				t.Errorf("Test %d: %s: Calculated Md5 different from the actual one %s.", i+1, instanceType, objInfo.MD5Sum)
+			if testCase.inputMeta["etag"] != objInfo.ETag {
+				t.Errorf("Test %d: %s: Calculated Md5 different from the actual one %s.", i+1, instanceType, objInfo.ETag)
 			}
 		}
 	}
@@ -271,7 +271,7 @@ func testObjectAPIPutObjectDiskNotFound(obj ObjectLayer, instanceType string, di
 		bucket,
 		object,
 		[]byte("mnop"),
-		map[string]string{"md5Sum": "e132e96a5ddad6da8b07bba6f6131fef"},
+		map[string]string{"etag": "e132e96a5ddad6da8b07bba6f6131fef"},
 		int64(len("mnop")),
 		false,
 		"",
diff --git a/cmd/object-api-utils.go b/cmd/object-api-utils.go
index acb14f508..ec95c3250 100644
--- a/cmd/object-api-utils.go
+++ b/cmd/object-api-utils.go
@@ -187,6 +187,35 @@ func getCompleteMultipartMD5(parts []completePart) (string, error) {
 	return s3MD5, nil
 }
 
+// Clean meta etag keys 'md5Sum', 'etag'.
+func cleanMetaETag(metadata map[string]string) map[string]string {
+	return cleanMetadata(metadata, "md5Sum", "etag")
+}
+
+// Clean metadata takes keys to be filtered
+// and returns a new map with the keys filtered.
+func cleanMetadata(metadata map[string]string, keyNames ...string) map[string]string {
+	var newMeta = make(map[string]string)
+	for k, v := range metadata {
+		if contains(keyNames, k) {
+			continue
+		}
+		newMeta[k] = v
+	}
+	return newMeta
+}
+
+// Extracts etag value from the metadata.
+func extractETag(metadata map[string]string) string {
+	// md5Sum tag is kept for backward compatibility.
+	etag, ok := metadata["md5Sum"]
+	if !ok {
+		etag = metadata["etag"]
+	}
+	// Success.
+	return etag
+}
+
 // Prefix matcher string matches prefix in a platform specific way.
 // For example on windows since its case insensitive we are supposed
 // to do case insensitive checks.
diff --git a/cmd/object-handlers-common.go b/cmd/object-handlers-common.go
index 01f2ba2ae..68bfcb8be 100644
--- a/cmd/object-handlers-common.go
+++ b/cmd/object-handlers-common.go
@@ -59,8 +59,8 @@ func checkCopyObjectPreconditions(w http.ResponseWriter, r *http.Request, objInf
 		// set object-related metadata headers
 		w.Header().Set("Last-Modified", objInfo.ModTime.UTC().Format(http.TimeFormat))
 
-		if objInfo.MD5Sum != "" {
-			w.Header().Set("ETag", "\""+objInfo.MD5Sum+"\"")
+		if objInfo.ETag != "" {
+			w.Header().Set("ETag", "\""+objInfo.ETag+"\"")
 		}
 	}
 	// x-amz-copy-source-if-modified-since: Return the object only if it has been modified
@@ -95,7 +95,7 @@ func checkCopyObjectPreconditions(w http.ResponseWriter, r *http.Request, objInf
 	// same as the one specified; otherwise return a 412 (precondition failed).
 	ifMatchETagHeader := r.Header.Get("x-amz-copy-source-if-match")
 	if ifMatchETagHeader != "" {
-		if objInfo.MD5Sum != "" && !isETagEqual(objInfo.MD5Sum, ifMatchETagHeader) {
+		if objInfo.ETag != "" && !isETagEqual(objInfo.ETag, ifMatchETagHeader) {
 			// If the object ETag does not match with the specified ETag.
 			writeHeaders()
 			writeErrorResponse(w, ErrPreconditionFailed, r.URL)
@@ -107,7 +107,7 @@ func checkCopyObjectPreconditions(w http.ResponseWriter, r *http.Request, objInf
 	// one specified otherwise, return a 304 (not modified).
 	ifNoneMatchETagHeader := r.Header.Get("x-amz-copy-source-if-none-match")
 	if ifNoneMatchETagHeader != "" {
-		if objInfo.MD5Sum != "" && isETagEqual(objInfo.MD5Sum, ifNoneMatchETagHeader) {
+		if objInfo.ETag != "" && isETagEqual(objInfo.ETag, ifNoneMatchETagHeader) {
 			// If the object ETag matches with the specified ETag.
 			writeHeaders()
 			writeErrorResponse(w, ErrPreconditionFailed, r.URL)
@@ -144,8 +144,8 @@ func checkPreconditions(w http.ResponseWriter, r *http.Request, objInfo ObjectIn
 		// set object-related metadata headers
 		w.Header().Set("Last-Modified", objInfo.ModTime.UTC().Format(http.TimeFormat))
 
-		if objInfo.MD5Sum != "" {
-			w.Header().Set("ETag", "\""+objInfo.MD5Sum+"\"")
+		if objInfo.ETag != "" {
+			w.Header().Set("ETag", "\""+objInfo.ETag+"\"")
 		}
 	}
 	// If-Modified-Since : Return the object only if it has been modified since the specified time,
@@ -180,7 +180,7 @@ func checkPreconditions(w http.ResponseWriter, r *http.Request, objInfo ObjectIn
 	// otherwise return a 412 (precondition failed).
 	ifMatchETagHeader := r.Header.Get("If-Match")
 	if ifMatchETagHeader != "" {
-		if !isETagEqual(objInfo.MD5Sum, ifMatchETagHeader) {
+		if !isETagEqual(objInfo.ETag, ifMatchETagHeader) {
 			// If the object ETag does not match with the specified ETag.
 			writeHeaders()
 			writeErrorResponse(w, ErrPreconditionFailed, r.URL)
@@ -192,7 +192,7 @@ func checkPreconditions(w http.ResponseWriter, r *http.Request, objInfo ObjectIn
 	// one specified otherwise, return a 304 (not modified).
 	ifNoneMatchETagHeader := r.Header.Get("If-None-Match")
 	if ifNoneMatchETagHeader != "" {
-		if isETagEqual(objInfo.MD5Sum, ifNoneMatchETagHeader) {
+		if isETagEqual(objInfo.ETag, ifNoneMatchETagHeader) {
 			// If the object ETag matches with the specified ETag.
 			writeHeaders()
 			w.WriteHeader(http.StatusNotModified)
diff --git a/cmd/object-handlers.go b/cmd/object-handlers.go
index 108a6139e..bc432a097 100644
--- a/cmd/object-handlers.go
+++ b/cmd/object-handlers.go
@@ -360,10 +360,8 @@ func (api objectAPIHandlers) CopyObjectHandler(w http.ResponseWriter, r *http.Re
 
 	defaultMeta := objInfo.UserDefined
 
-	// Make sure to remove saved md5sum, object might have been uploaded
-	// as multipart which doesn't have a standard md5sum, we just let
-	// CopyObject calculate a new one.
-	delete(defaultMeta, "md5Sum")
+	// Make sure to remove saved etag, CopyObject calculates a new one.
+	delete(defaultMeta, "etag")
 
 	newMetadata := getCpObjMetadataFromHeader(r.Header, defaultMeta)
 	// Check if x-amz-metadata-directive was not set to REPLACE and source,
@@ -383,8 +381,7 @@ func (api objectAPIHandlers) CopyObjectHandler(w http.ResponseWriter, r *http.Re
 		return
 	}
 
-	md5Sum := objInfo.MD5Sum
-	response := generateCopyObjectResponse(md5Sum, objInfo.ModTime)
+	response := generateCopyObjectResponse(objInfo.ETag, objInfo.ModTime)
 	encodedSuccessResponse := encodeResponse(response)
 
 	// Write success response.
@@ -482,7 +479,7 @@ func (api objectAPIHandlers) PutObjectHandler(w http.ResponseWriter, r *http.Req
 	}
 
 	// Make sure we hex encode md5sum here.
-	metadata["md5Sum"] = hex.EncodeToString(md5Bytes)
+	metadata["etag"] = hex.EncodeToString(md5Bytes)
 
 	sha256sum := ""
 
@@ -540,7 +537,7 @@ func (api objectAPIHandlers) PutObjectHandler(w http.ResponseWriter, r *http.Req
 		writeErrorResponse(w, toAPIErrorCode(err), r.URL)
 		return
 	}
-	w.Header().Set("ETag", "\""+objInfo.MD5Sum+"\"")
+	w.Header().Set("ETag", "\""+objInfo.ETag+"\"")
 	writeSuccessResponseHeadersOnly(w)
 
 	// Get host and port from Request.RemoteAddr.
@@ -965,7 +962,7 @@ func (api objectAPIHandlers) CompleteMultipartUploadHandler(w http.ResponseWrite
 	// Get object location.
 	location := getLocation(r)
 	// Generate complete multipart response.
-	response := generateCompleteMultpartUploadResponse(bucket, object, location, objInfo.MD5Sum)
+	response := generateCompleteMultpartUploadResponse(bucket, object, location, objInfo.ETag)
 	encodedSuccessResponse := encodeResponse(response)
 	if err != nil {
 		errorIf(err, "Unable to parse CompleteMultipartUpload response")
@@ -974,7 +971,7 @@ func (api objectAPIHandlers) CompleteMultipartUploadHandler(w http.ResponseWrite
 	}
 
 	// Set etag.
-	w.Header().Set("ETag", "\""+objInfo.MD5Sum+"\"")
+	w.Header().Set("ETag", "\""+objInfo.ETag+"\"")
 
 	// Write success response.
 	writeSuccessResponseXML(w, encodedSuccessResponse)
diff --git a/cmd/object_api_suite_test.go b/cmd/object_api_suite_test.go
index 3f0af2d25..4fe4661ca 100644
--- a/cmd/object_api_suite_test.go
+++ b/cmd/object_api_suite_test.go
@@ -104,14 +104,14 @@ func testMultipartObjectCreation(obj ObjectLayer, instanceType string, c TestErr
 	data := bytes.Repeat([]byte("0123456789abcdef"), 5*humanize.MiByte/16)
 	completedParts := completeMultipartUpload{}
 	for i := 1; i <= 10; i++ {
-		expectedMD5Sumhex := getMD5Hash(data)
+		expectedETaghex := getMD5Hash(data)
 
 		var calcPartInfo PartInfo
-		calcPartInfo, err = obj.PutObjectPart("bucket", "key", uploadID, i, int64(len(data)), bytes.NewBuffer(data), expectedMD5Sumhex, "")
+		calcPartInfo, err = obj.PutObjectPart("bucket", "key", uploadID, i, int64(len(data)), bytes.NewBuffer(data), expectedETaghex, "")
 		if err != nil {
 			c.Errorf("%s: <ERROR> %s", instanceType, err)
 		}
-		if calcPartInfo.ETag != expectedMD5Sumhex {
+		if calcPartInfo.ETag != expectedETaghex {
 			c.Errorf("MD5 Mismatch")
 		}
 		completedParts.Parts = append(completedParts.Parts, completePart{
@@ -123,7 +123,7 @@ func testMultipartObjectCreation(obj ObjectLayer, instanceType string, c TestErr
 	if err != nil {
 		c.Fatalf("%s: <ERROR> %s", instanceType, err)
 	}
-	if objInfo.MD5Sum != "7d364cb728ce42a74a96d22949beefb2-10" {
+	if objInfo.ETag != "7d364cb728ce42a74a96d22949beefb2-10" {
 		c.Errorf("Md5 mismtch")
 	}
 }
@@ -153,18 +153,18 @@ func testMultipartObjectAbort(obj ObjectLayer, instanceType string, c TestErrHan
 			randomString = randomString + strconv.Itoa(num)
 		}
 
-		expectedMD5Sumhex := getMD5Hash([]byte(randomString))
+		expectedETaghex := getMD5Hash([]byte(randomString))
 
-		metadata["md5"] = expectedMD5Sumhex
+		metadata["md5"] = expectedETaghex
 		var calcPartInfo PartInfo
-		calcPartInfo, err = obj.PutObjectPart("bucket", "key", uploadID, i, int64(len(randomString)), bytes.NewBufferString(randomString), expectedMD5Sumhex, "")
+		calcPartInfo, err = obj.PutObjectPart("bucket", "key", uploadID, i, int64(len(randomString)), bytes.NewBufferString(randomString), expectedETaghex, "")
 		if err != nil {
 			c.Fatalf("%s: <ERROR> %s", instanceType, err)
 		}
-		if calcPartInfo.ETag != expectedMD5Sumhex {
+		if calcPartInfo.ETag != expectedETaghex {
 			c.Errorf("Md5 Mismatch")
 		}
-		parts[i] = expectedMD5Sumhex
+		parts[i] = expectedETaghex
 	}
 	err = obj.AbortMultipartUpload("bucket", "key", uploadID)
 	if err != nil {
@@ -191,18 +191,18 @@ func testMultipleObjectCreation(obj ObjectLayer, instanceType string, c TestErrH
 			randomString = randomString + strconv.Itoa(num)
 		}
 
-		expectedMD5Sumhex := getMD5Hash([]byte(randomString))
+		expectedETaghex := getMD5Hash([]byte(randomString))
 
 		key := "obj" + strconv.Itoa(i)
 		objects[key] = []byte(randomString)
 		metadata := make(map[string]string)
-		metadata["md5Sum"] = expectedMD5Sumhex
+		metadata["etag"] = expectedETaghex
 		var objInfo ObjectInfo
 		objInfo, err = obj.PutObject("bucket", key, int64(len(randomString)), bytes.NewBufferString(randomString), metadata, "")
 		if err != nil {
 			c.Fatalf("%s: <ERROR> %s", instanceType, err)
 		}
-		if objInfo.MD5Sum != expectedMD5Sumhex {
+		if objInfo.ETag != expectedETaghex {
 			c.Errorf("Md5 Mismatch")
 		}
 	}
diff --git a/cmd/server_test.go b/cmd/server_test.go
index a3222d499..8f607c142 100644
--- a/cmd/server_test.go
+++ b/cmd/server_test.go
@@ -1151,7 +1151,7 @@ func (s *TestSuiteCommon) TestPutObject(c *C) {
 	c.Assert(err, IsNil)
 	c.Assert(response.StatusCode, Equals, http.StatusOK)
 	// The response Etag header should contain Md5sum of an empty string.
-	c.Assert(response.Header.Get("Etag"), Equals, "\""+emptyStrMd5Sum+"\"")
+	c.Assert(response.Header.Get("Etag"), Equals, "\""+emptyETag+"\"")
 }
 
 // TestListBuckets - Make request for listing of all buckets.
@@ -1841,7 +1841,7 @@ func (s *TestSuiteCommon) TestGetObjectLarge11MiB(c *C) {
 	getContent, err := ioutil.ReadAll(response.Body)
 	c.Assert(err, IsNil)
 
-	// Get md5Sum of the response content.
+	// Get etag of the response content.
 	getMD5 := getMD5Hash(getContent)
 
 	// Compare putContent and getContent.
@@ -2505,8 +2505,8 @@ func (s *TestSuiteCommon) TestObjectValidMD5(c *C) {
 	// Create a byte array of 5MB.
 	// content for the object to be uploaded.
 	data := bytes.Repeat([]byte("0123456789abcdef"), 5*humanize.MiByte/16)
-	// calculate md5Sum of the data.
-	md5SumBase64 := getMD5HashBase64(data)
+	// calculate etag of the data.
+	etagBase64 := getMD5HashBase64(data)
 
 	buffer1 := bytes.NewReader(data)
 	objectName := "test-1-object"
@@ -2515,7 +2515,7 @@ func (s *TestSuiteCommon) TestObjectValidMD5(c *C) {
 		int64(buffer1.Len()), buffer1, s.accessKey, s.secretKey, s.signer)
 	c.Assert(err, IsNil)
 	// set the Content-Md5 to be the hash to content.
-	request.Header.Set("Content-Md5", md5SumBase64)
+	request.Header.Set("Content-Md5", etagBase64)
 	client = http.Client{Transport: s.transport}
 	response, err = client.Do(request)
 	c.Assert(err, IsNil)
@@ -2578,14 +2578,14 @@ func (s *TestSuiteCommon) TestObjectMultipart(c *C) {
 	// content for the part to be uploaded.
 	// Create a byte array of 5MB.
 	data := bytes.Repeat([]byte("0123456789abcdef"), 5*humanize.MiByte/16)
-	// calculate md5Sum of the data.
+	// calculate etag of the data.
 	md5SumBase64 := getMD5HashBase64(data)
 
 	buffer1 := bytes.NewReader(data)
 	// HTTP request for the part to be uploaded.
 	request, err = newTestSignedRequest("PUT", getPartUploadURL(s.endPoint, bucketName, objectName, uploadID, "1"),
 		int64(buffer1.Len()), buffer1, s.accessKey, s.secretKey, s.signer)
-	// set the Content-Md5 header to the base64 encoding the md5Sum of the content.
+	// set the Content-Md5 header to the base64 encoding the etag of the content.
 	request.Header.Set("Content-Md5", md5SumBase64)
 	c.Assert(err, IsNil)
 
@@ -2599,14 +2599,14 @@ func (s *TestSuiteCommon) TestObjectMultipart(c *C) {
 	// Create a byte array of 1 byte.
 	data = []byte("0")
 
-	// calculate md5Sum of the data.
+	// calculate etag of the data.
 	md5SumBase64 = getMD5HashBase64(data)
 
 	buffer2 := bytes.NewReader(data)
 	// HTTP request for the second part to be uploaded.
 	request, err = newTestSignedRequest("PUT", getPartUploadURL(s.endPoint, bucketName, objectName, uploadID, "2"),
 		int64(buffer2.Len()), buffer2, s.accessKey, s.secretKey, s.signer)
-	// set the Content-Md5 header to the base64 encoding the md5Sum of the content.
+	// set the Content-Md5 header to the base64 encoding the etag of the content.
 	request.Header.Set("Content-Md5", md5SumBase64)
 	c.Assert(err, IsNil)
 
diff --git a/cmd/web-handlers_test.go b/cmd/web-handlers_test.go
index 2520d20c5..4120aa4c0 100644
--- a/cmd/web-handlers_test.go
+++ b/cmd/web-handlers_test.go
@@ -370,7 +370,7 @@ func testListObjectsWebHandler(obj ObjectLayer, instanceType string, t TestErrHa
 
 	data := bytes.Repeat([]byte("a"), objectSize)
 
-	_, err = obj.PutObject(bucketName, objectName, int64(len(data)), bytes.NewReader(data), map[string]string{"md5Sum": "c9a34cfc85d982698c6ac89f76071abd"}, "")
+	_, err = obj.PutObject(bucketName, objectName, int64(len(data)), bytes.NewReader(data), map[string]string{"etag": "c9a34cfc85d982698c6ac89f76071abd"}, "")
 
 	if err != nil {
 		t.Fatalf("Was not able to upload an object, %v", err)
@@ -465,14 +465,14 @@ func testRemoveObjectWebHandler(obj ObjectLayer, instanceType string, t TestErrH
 	data := bytes.Repeat([]byte("a"), objectSize)
 
 	_, err = obj.PutObject(bucketName, objectName, int64(len(data)), bytes.NewReader(data),
-		map[string]string{"md5Sum": "c9a34cfc85d982698c6ac89f76071abd"}, "")
+		map[string]string{"etag": "c9a34cfc85d982698c6ac89f76071abd"}, "")
 	if err != nil {
 		t.Fatalf("Was not able to upload an object, %v", err)
 	}
 
 	objectName = "a/object"
 	_, err = obj.PutObject(bucketName, objectName, int64(len(data)), bytes.NewReader(data),
-		map[string]string{"md5Sum": "c9a34cfc85d982698c6ac89f76071abd"}, "")
+		map[string]string{"etag": "c9a34cfc85d982698c6ac89f76071abd"}, "")
 	if err != nil {
 		t.Fatalf("Was not able to upload an object, %v", err)
 	}
@@ -788,7 +788,7 @@ func testDownloadWebHandler(obj ObjectLayer, instanceType string, t TestErrHandl
 	}
 
 	content := []byte("temporary file's content")
-	_, err = obj.PutObject(bucketName, objectName, int64(len(content)), bytes.NewReader(content), map[string]string{"md5Sum": "01ce59706106fe5e02e7f55fffda7f34"}, "")
+	_, err = obj.PutObject(bucketName, objectName, int64(len(content)), bytes.NewReader(content), map[string]string{"etag": "01ce59706106fe5e02e7f55fffda7f34"}, "")
 	if err != nil {
 		t.Fatalf("Was not able to upload an object, %v", err)
 	}
@@ -940,7 +940,7 @@ func testWebPresignedGetHandler(obj ObjectLayer, instanceType string, t TestErrH
 	}
 
 	data := bytes.Repeat([]byte("a"), objectSize)
-	_, err = obj.PutObject(bucketName, objectName, int64(len(data)), bytes.NewReader(data), map[string]string{"md5Sum": "c9a34cfc85d982698c6ac89f76071abd"}, "")
+	_, err = obj.PutObject(bucketName, objectName, int64(len(data)), bytes.NewReader(data), map[string]string{"etag": "c9a34cfc85d982698c6ac89f76071abd"}, "")
 	if err != nil {
 		t.Fatalf("Was not able to upload an object, %v", err)
 	}
diff --git a/cmd/xl-v1-metadata.go b/cmd/xl-v1-metadata.go
index cc3647598..429cc8f8e 100644
--- a/cmd/xl-v1-metadata.go
+++ b/cmd/xl-v1-metadata.go
@@ -146,7 +146,10 @@ type xlMetaV1 struct {
 // XL metadata constants.
 const (
 	// XL meta version.
-	xlMetaVersion = "1.0.0"
+	xlMetaVersion = "1.0.1"
+
+	// XL meta version.
+	xlMetaVersion100 = "1.0.0"
 
 	// XL meta format string.
 	xlMetaFormat = "xl"
@@ -173,7 +176,38 @@ func newXLMetaV1(object string, dataBlocks, parityBlocks int) (xlMeta xlMetaV1)
 // IsValid - tells if the format is sane by validating the version
 // string and format style.
 func (m xlMetaV1) IsValid() bool {
-	return m.Version == xlMetaVersion && m.Format == xlMetaFormat
+	return isXLMetaValid(m.Version, m.Format)
+}
+
+// Verifies if the backend format metadata is sane by validating
+// the version string and format style.
+func isXLMetaValid(version, format string) bool {
+	return ((version == xlMetaVersion || version == xlMetaVersion100) &&
+		format == xlMetaFormat)
+}
+
+// Converts metadata to object info.
+func (m xlMetaV1) ToObjectInfo(bucket, object string) ObjectInfo {
+	objInfo := ObjectInfo{
+		IsDir:           false,
+		Bucket:          bucket,
+		Name:            object,
+		Size:            m.Stat.Size,
+		ModTime:         m.Stat.ModTime,
+		ContentType:     m.Meta["content-type"],
+		ContentEncoding: m.Meta["content-encoding"],
+	}
+
+	// Extract etag from metadata.
+	objInfo.ETag = extractETag(m.Meta)
+
+	// etag/md5Sum has already been extracted. We need to
+	// remove to avoid it from appearing as part of
+	// response headers. e.g, X-Minio-* or X-Amz-*.
+	objInfo.UserDefined = cleanMetaETag(m.Meta)
+
+	// Success.
+	return objInfo
 }
 
 // objectPartIndex - returns the index of matching object part number.
diff --git a/cmd/xl-v1-multipart.go b/cmd/xl-v1-multipart.go
index b2a2b6b52..7f266f1d1 100644
--- a/cmd/xl-v1-multipart.go
+++ b/cmd/xl-v1-multipart.go
@@ -973,7 +973,7 @@ func (xl xlObjects) CompleteMultipartUpload(bucket string, object string, upload
 	xlMeta.Stat.ModTime = UTCNow()
 
 	// Save successfully calculated md5sum.
-	xlMeta.Meta["md5Sum"] = s3MD5
+	xlMeta.Meta["etag"] = s3MD5
 	uploadIDPath = path.Join(bucket, object, uploadID)
 	tempUploadIDPath := uploadID
 
@@ -1061,7 +1061,7 @@ func (xl xlObjects) CompleteMultipartUpload(bucket string, object string, upload
 		Name:            object,
 		Size:            xlMeta.Stat.Size,
 		ModTime:         xlMeta.Stat.ModTime,
-		MD5Sum:          xlMeta.Meta["md5Sum"],
+		ETag:            xlMeta.Meta["etag"],
 		ContentType:     xlMeta.Meta["content-type"],
 		ContentEncoding: xlMeta.Meta["content-encoding"],
 		UserDefined:     xlMeta.Meta,
diff --git a/cmd/xl-v1-object.go b/cmd/xl-v1-object.go
index d7b041387..31bb2bfa6 100644
--- a/cmd/xl-v1-object.go
+++ b/cmd/xl-v1-object.go
@@ -101,23 +101,7 @@ func (xl xlObjects) CopyObject(srcBucket, srcObject, dstBucket, dstObject string
 		if err = renameXLMetadata(onlineDisks, minioMetaTmpBucket, tempObj, srcBucket, srcObject, xl.writeQuorum); err != nil {
 			return ObjectInfo{}, toObjectErr(err, srcBucket, srcObject)
 		}
-
-		objInfo := ObjectInfo{
-			IsDir:           false,
-			Bucket:          srcBucket,
-			Name:            srcObject,
-			Size:            xlMeta.Stat.Size,
-			ModTime:         xlMeta.Stat.ModTime,
-			MD5Sum:          xlMeta.Meta["md5Sum"],
-			ContentType:     xlMeta.Meta["content-type"],
-			ContentEncoding: xlMeta.Meta["content-encoding"],
-		}
-		// md5Sum has already been extracted into objInfo.MD5Sum.  We
-		// need to remove it from xlMetaMap to avoid it from appearing as
-		// part of response headers. e.g, X-Minio-* or X-Amz-*.
-		delete(xlMeta.Meta, "md5Sum")
-		objInfo.UserDefined = xlMeta.Meta
-		return objInfo, nil
+		return xlMeta.ToObjectInfo(srcBucket, srcObject), nil
 	}
 
 	// Initialize pipe.
@@ -333,10 +317,9 @@ func (xl xlObjects) GetObjectInfo(bucket, object string) (ObjectInfo, error) {
 
 // getObjectInfo - wrapper for reading object metadata and constructs ObjectInfo.
 func (xl xlObjects) getObjectInfo(bucket, object string) (objInfo ObjectInfo, err error) {
-	// returns xl meta map and stat info.
+	// Extracts xlStat and xlMetaMap.
 	xlStat, xlMetaMap, err := xl.readXLMetaStat(bucket, object)
 	if err != nil {
-		// Return error.
 		return ObjectInfo{}, err
 	}
 
@@ -346,17 +329,19 @@ func (xl xlObjects) getObjectInfo(bucket, object string) (objInfo ObjectInfo, er
 		Name:            object,
 		Size:            xlStat.Size,
 		ModTime:         xlStat.ModTime,
-		MD5Sum:          xlMetaMap["md5Sum"],
 		ContentType:     xlMetaMap["content-type"],
 		ContentEncoding: xlMetaMap["content-encoding"],
 	}
 
-	// md5Sum has already been extracted into objInfo.MD5Sum.  We
-	// need to remove it from xlMetaMap to avoid it from appearing as
-	// part of response headers. e.g, X-Minio-* or X-Amz-*.
+	// Extract etag.
+	objInfo.ETag = extractETag(xlMetaMap)
 
-	delete(xlMetaMap, "md5Sum")
-	objInfo.UserDefined = xlMetaMap
+	// etag/md5Sum has already been extracted. We need to
+	// remove to avoid it from appearing as part of
+	// response headers. e.g, X-Minio-* or X-Amz-*.
+	objInfo.UserDefined = cleanMetaETag(xlMetaMap)
+
+	// Success.
 	return objInfo, nil
 }
 
@@ -650,8 +635,8 @@ func (xl xlObjects) PutObject(bucket string, object string, size int64, data io.
 
 	newMD5Hex := hex.EncodeToString(md5Writer.Sum(nil))
 	// Update the md5sum if not set with the newly calculated one.
-	if len(metadata["md5Sum"]) == 0 {
-		metadata["md5Sum"] = newMD5Hex
+	if len(metadata["etag"]) == 0 {
+		metadata["etag"] = newMD5Hex
 	}
 
 	// Guess content-type from the extension if possible.
@@ -664,7 +649,7 @@ func (xl xlObjects) PutObject(bucket string, object string, size int64, data io.
 	}
 
 	// md5Hex representation.
-	md5Hex := metadata["md5Sum"]
+	md5Hex := metadata["etag"]
 	if md5Hex != "" {
 		if newMD5Hex != md5Hex {
 			// Returns md5 mismatch.
@@ -730,7 +715,7 @@ func (xl xlObjects) PutObject(bucket string, object string, size int64, data io.
 		Name:            object,
 		Size:            xlMeta.Stat.Size,
 		ModTime:         xlMeta.Stat.ModTime,
-		MD5Sum:          xlMeta.Meta["md5Sum"],
+		ETag:            xlMeta.Meta["etag"],
 		ContentType:     xlMeta.Meta["content-type"],
 		ContentEncoding: xlMeta.Meta["content-encoding"],
 		UserDefined:     xlMeta.Meta,
diff --git a/cmd/xl-v1-utils.go b/cmd/xl-v1-utils.go
index 283b690ad..95f4cdb1d 100644
--- a/cmd/xl-v1-utils.go
+++ b/cmd/xl-v1-utils.go
@@ -253,6 +253,19 @@ func readXLMetaStat(disk StorageAPI, bucket string, object string) (statInfo, ma
 	if err != nil {
 		return statInfo{}, nil, traceError(err)
 	}
+
+	// obtain version.
+	xlVersion := parseXLVersion(xlMetaBuf)
+
+	// obtain format.
+	xlFormat := parseXLFormat(xlMetaBuf)
+
+	// Validate if the xl.json we read is sane, return corrupted format.
+	if !isXLMetaValid(xlVersion, xlFormat) {
+		// For version mismatchs and unrecognized format, return corrupted format.
+		return statInfo{}, nil, traceError(errCorruptedFormat)
+	}
+
 	// obtain xlMetaV1{}.Meta using `github.com/tidwall/gjson`.
 	xlMetaMap := parseXLMetaMap(xlMetaBuf)
 
@@ -261,6 +274,7 @@ func readXLMetaStat(disk StorageAPI, bucket string, object string) (statInfo, ma
 	if err != nil {
 		return statInfo{}, nil, traceError(err)
 	}
+
 	// Return structured `xl.json`.
 	return xlStat, xlMetaMap, nil
 }
diff --git a/docs/backend/fs/fs.json b/docs/backend/fs/fs.json
index 6b309dde3..7eda41dcb 100644
--- a/docs/backend/fs/fs.json
+++ b/docs/backend/fs/fs.json
@@ -5,6 +5,7 @@
         "release": "DEVELOPMENT.GOGET"
     },
     "meta": {
+        "etag": "97586a5290d4f5a41328062d6a7da593-3",
         "content-type": "binary/octet-stream",
         "content-encoding": "gzip"
     },
diff --git a/docs/backend/xl/xl.json b/docs/backend/xl/xl.json
index 9cdc3ca06..6b37f0799 100644
--- a/docs/backend/xl/xl.json
+++ b/docs/backend/xl/xl.json
@@ -14,7 +14,7 @@
         }
     ],
     "meta": {
-        "md5Sum": "97586a5290d4f5a41328062d6a7da593-3",
+        "etag": "97586a5290d4f5a41328062d6a7da593-3",
         "content-type": "application\/octet-stream",
         "content-encoding": "gzip"
     },