diff --git a/api-headers.go b/api-headers.go
index ba9ecaecd..8099d32de 100644
--- a/api-headers.go
+++ b/api-headers.go
@@ -79,8 +79,8 @@ func setObjectHeaders(w http.ResponseWriter, metadata fs.ObjectMetadata, content
 	lastModified := metadata.Created.Format(http.TimeFormat)
 	// object related headers
 	w.Header().Set("Content-Type", metadata.ContentType)
-	if metadata.Md5 != "" {
-		w.Header().Set("ETag", "\""+metadata.Md5+"\"")
+	if metadata.MD5 != "" {
+		w.Header().Set("ETag", "\""+metadata.MD5+"\"")
 	}
 	w.Header().Set("Last-Modified", lastModified)
 
diff --git a/api-response.go b/api-response.go
index e294e7ffe..e033668da 100644
--- a/api-response.go
+++ b/api-response.go
@@ -108,8 +108,8 @@ func generateListObjectsResponse(bucket, prefix, marker, delimiter string, maxKe
 		}
 		content.Key = object.Object
 		content.LastModified = object.Created.Format(rfcFormat)
-		if object.Md5 != "" {
-			content.ETag = "\"" + object.Md5 + "\""
+		if object.MD5 != "" {
+			content.ETag = "\"" + object.MD5 + "\""
 		}
 		content.Size = object.Size
 		content.StorageClass = "STANDARD"
diff --git a/bucket-handlers.go b/bucket-handlers.go
index c9de6505b..546cfefc6 100644
--- a/bucket-handlers.go
+++ b/bucket-handlers.go
@@ -353,8 +353,8 @@ func (api CloudStorageAPI) PostPolicyBucketHandler(w http.ResponseWriter, req *h
 		}
 		return
 	}
-	if metadata.Md5 != "" {
-		w.Header().Set("ETag", "\""+metadata.Md5+"\"")
+	if metadata.MD5 != "" {
+		w.Header().Set("ETag", "\""+metadata.MD5+"\"")
 	}
 	writeSuccessResponse(w, nil)
 }
diff --git a/object-handlers.go b/object-handlers.go
index 68217810f..2195ca76d 100644
--- a/object-handlers.go
+++ b/object-handlers.go
@@ -198,8 +198,8 @@ func (api CloudStorageAPI) PutObjectHandler(w http.ResponseWriter, req *http.Req
 		}
 		return
 	}
-	if metadata.Md5 != "" {
-		w.Header().Set("ETag", "\""+metadata.Md5+"\"")
+	if metadata.MD5 != "" {
+		w.Header().Set("ETag", "\""+metadata.MD5+"\"")
 	}
 	writeSuccessResponse(w, nil)
 }
@@ -501,7 +501,7 @@ func (api CloudStorageAPI) CompleteMultipartUploadHandler(w http.ResponseWriter,
 		}
 		return
 	}
-	response := generateCompleteMultpartUploadResponse(bucket, object, req.URL.String(), metadata.Md5)
+	response := generateCompleteMultpartUploadResponse(bucket, object, req.URL.String(), metadata.MD5)
 	encodedSuccessResponse := encodeSuccessResponse(response)
 	// write headers
 	setCommonHeaders(w)
diff --git a/pkg/fs/api_suite_nix_test.go b/pkg/fs/api_suite_nix_test.go
index 61e1ef83d..40f60f7d5 100644
--- a/pkg/fs/api_suite_nix_test.go
+++ b/pkg/fs/api_suite_nix_test.go
@@ -92,7 +92,7 @@ func testMultipartObjectCreation(c *check.C, create func() Filesystem) {
 	c.Assert(e, check.IsNil)
 	objectMetadata, err := fs.CompleteMultipartUpload("bucket", "key", uploadID, bytes.NewReader(completedPartsBytes), nil)
 	c.Assert(err, check.IsNil)
-	c.Assert(objectMetadata.Md5, check.Equals, finalExpectedmd5SumHex)
+	c.Assert(objectMetadata.MD5, check.Equals, finalExpectedmd5SumHex)
 }
 
 func testMultipartObjectAbort(c *check.C, create func() Filesystem) {
@@ -147,7 +147,7 @@ func testMultipleObjectCreation(c *check.C, create func() Filesystem) {
 		objects[key] = []byte(randomString)
 		objectMetadata, err := fs.CreateObject("bucket", key, expectedmd5Sum, int64(len(randomString)), bytes.NewBufferString(randomString), nil)
 		c.Assert(err, check.IsNil)
-		c.Assert(objectMetadata.Md5, check.Equals, expectedmd5Sumhex)
+		c.Assert(objectMetadata.MD5, check.Equals, expectedmd5Sumhex)
 	}
 
 	for key, value := range objects {
@@ -276,7 +276,7 @@ func testObjectOverwriteWorks(c *check.C, create func() Filesystem) {
 	md5Sum1hex := hex.EncodeToString(hasher1.Sum(nil))
 	objectMetadata, err := fs.CreateObject("bucket", "object", md5Sum1, int64(len("one")), bytes.NewBufferString("one"), nil)
 	c.Assert(err, check.IsNil)
-	c.Assert(md5Sum1hex, check.Equals, objectMetadata.Md5)
+	c.Assert(md5Sum1hex, check.Equals, objectMetadata.MD5)
 
 	hasher2 := md5.New()
 	hasher2.Write([]byte("three"))
@@ -326,7 +326,7 @@ func testPutObjectInSubdir(c *check.C, create func() Filesystem) {
 	md5Sum1hex := hex.EncodeToString(hasher.Sum(nil))
 	objectMetadata, err := fs.CreateObject("bucket", "dir1/dir2/object", md5Sum1, int64(len("hello world")), bytes.NewBufferString("hello world"), nil)
 	c.Assert(err, check.IsNil)
-	c.Assert(objectMetadata.Md5, check.Equals, md5Sum1hex)
+	c.Assert(objectMetadata.MD5, check.Equals, md5Sum1hex)
 
 	var bytesBuffer bytes.Buffer
 	length, err := fs.GetObject(&bytesBuffer, "bucket", "dir1/dir2/object", 0, 0)
@@ -458,7 +458,7 @@ func testDefaultContentType(c *check.C, create func() Filesystem) {
 	c.Assert(metadata.ContentType, check.Equals, "application/octet-stream")
 }
 
-func testContentMd5Set(c *check.C, create func() Filesystem) {
+func testContentMD5Set(c *check.C, create func() Filesystem) {
 	fs := create()
 	err := fs.MakeBucket("bucket", "")
 	c.Assert(err, check.IsNil)
diff --git a/pkg/fs/api_suite_windows_test.go b/pkg/fs/api_suite_windows_test.go
index 45ececdef..574ce69dc 100644
--- a/pkg/fs/api_suite_windows_test.go
+++ b/pkg/fs/api_suite_windows_test.go
@@ -91,7 +91,7 @@ func testMultipartObjectCreation(c *check.C, create func() Filesystem) {
 	c.Assert(e, check.IsNil)
 	objectMetadata, err := fs.CompleteMultipartUpload("bucket", "key", uploadID, bytes.NewReader(completedPartsBytes), nil)
 	c.Assert(err, check.IsNil)
-	c.Assert(objectMetadata.Md5, check.Equals, finalExpectedmd5SumHex)
+	c.Assert(objectMetadata.MD5, check.Equals, finalExpectedmd5SumHex)
 }
 
 func testMultipartObjectAbort(c *check.C, create func() Filesystem) {
@@ -146,7 +146,7 @@ func testMultipleObjectCreation(c *check.C, create func() Filesystem) {
 		objects[key] = []byte(randomString)
 		objectMetadata, err := fs.CreateObject("bucket", key, expectedmd5Sum, int64(len(randomString)), bytes.NewBufferString(randomString), nil)
 		c.Assert(err, check.IsNil)
-		c.Assert(objectMetadata.Md5, check.Equals, expectedmd5Sumhex)
+		c.Assert(objectMetadata.MD5, check.Equals, expectedmd5Sumhex)
 	}
 
 	for key, value := range objects {
@@ -273,7 +273,7 @@ func testObjectOverwriteWorks(c *check.C, create func() Filesystem) {
 	md5Sum1hex := hex.EncodeToString(hasher1.Sum(nil))
 	objectMetadata, err := fs.CreateObject("bucket", "object", md5Sum1, int64(len("one")), bytes.NewBufferString("one"), nil)
 	c.Assert(err, check.IsNil)
-	c.Assert(md5Sum1hex, check.Equals, objectMetadata.Md5)
+	c.Assert(md5Sum1hex, check.Equals, objectMetadata.MD5)
 
 	hasher2 := md5.New()
 	hasher2.Write([]byte("three"))
@@ -323,7 +323,7 @@ func testPutObjectInSubdir(c *check.C, create func() Filesystem) {
 	md5Sum1hex := hex.EncodeToString(hasher.Sum(nil))
 	objectMetadata, err := fs.CreateObject("bucket", "dir1/dir2/object", md5Sum1, int64(len("hello world")), bytes.NewBufferString("hello world"), nil)
 	c.Assert(err, check.IsNil)
-	c.Assert(objectMetadata.Md5, check.Equals, md5Sum1hex)
+	c.Assert(objectMetadata.MD5, check.Equals, md5Sum1hex)
 
 	var bytesBuffer bytes.Buffer
 	length, err := fs.GetObject(&bytesBuffer, "bucket", "dir1/dir2/object", 0, 0)
@@ -459,7 +459,7 @@ func testDefaultContentType(c *check.C, create func() Filesystem) {
 	c.Assert(metadata.ContentType, check.Equals, "application/octet-stream")
 }
 
-func testContentMd5Set(c *check.C, create func() Filesystem) {
+func testContentMD5Set(c *check.C, create func() Filesystem) {
 	fs := create()
 	err := fs.MakeBucket("bucket", "")
 	c.Assert(err, check.IsNil)
diff --git a/pkg/fs/config.go b/pkg/fs/config.go
index 339cfe156..ea8aa3baf 100644
--- a/pkg/fs/config.go
+++ b/pkg/fs/config.go
@@ -17,77 +17,42 @@
 package fs
 
 import (
-	"path/filepath"
-
 	"github.com/minio/minio-xl/pkg/probe"
 	"github.com/minio/minio-xl/pkg/quick"
-	"github.com/minio/minio/pkg/user"
 )
 
-func getFSBucketsConfigPath() (string, *probe.Error) {
-	if customBucketsConfigPath != "" {
-		return customBucketsConfigPath, nil
-	}
-	homeDir, e := user.HomeDir()
-	if e != nil {
-		return "", probe.NewError(e)
-	}
-	fsBucketsConfigPath := filepath.Join(homeDir, ".minio", "$buckets.json")
-	return fsBucketsConfigPath, nil
-}
+var multipartsMetadataPath, bucketsMetadataPath string
 
-func getFSMultipartsSessionConfigPath() (string, *probe.Error) {
-	if customMultipartsConfigPath != "" {
-		return customMultipartsConfigPath, nil
-	}
-	homeDir, e := user.HomeDir()
-	if e != nil {
-		return "", probe.NewError(e)
-	}
-	fsMultipartsConfigPath := filepath.Join(homeDir, ".minio", "$multiparts-session.json")
-	return fsMultipartsConfigPath, nil
+// setFSBucketsMetadataPath - set fs buckets metadata path.
+func setFSBucketsMetadataPath(metadataPath string) {
+	bucketsMetadataPath = metadataPath
 }
 
-// internal variable only accessed via get/set methods
-var customMultipartsConfigPath, customBucketsConfigPath string
-
-// setFSBucketsConfigPath - set custom fs buckets config path
-func setFSBucketsConfigPath(configPath string) {
-	customBucketsConfigPath = configPath
-}
-
-// SetFSMultipartsConfigPath - set custom multiparts session config path
-func setFSMultipartsConfigPath(configPath string) {
-	customMultipartsConfigPath = configPath
+// SetFSMultipartsMetadataPath - set custom multiparts session
+// metadata path.
+func setFSMultipartsMetadataPath(metadataPath string) {
+	multipartsMetadataPath = metadataPath
 }
 
 // saveMultipartsSession - save multiparts
-func saveMultipartsSession(multiparts *Multiparts) *probe.Error {
-	fsMultipartsConfigPath, err := getFSMultipartsSessionConfigPath()
-	if err != nil {
-		return err.Trace()
-	}
+func saveMultipartsSession(multiparts Multiparts) *probe.Error {
 	qc, err := quick.New(multiparts)
 	if err != nil {
 		return err.Trace()
 	}
-	if err := qc.Save(fsMultipartsConfigPath); err != nil {
+	if err := qc.Save(multipartsMetadataPath); err != nil {
 		return err.Trace()
 	}
 	return nil
 }
 
 // saveBucketsMetadata - save metadata of all buckets
-func saveBucketsMetadata(buckets *Buckets) *probe.Error {
-	fsBucketsConfigPath, err := getFSBucketsConfigPath()
-	if err != nil {
-		return err.Trace()
-	}
+func saveBucketsMetadata(buckets Buckets) *probe.Error {
 	qc, err := quick.New(buckets)
 	if err != nil {
 		return err.Trace()
 	}
-	if err := qc.Save(fsBucketsConfigPath); err != nil {
+	if err := qc.Save(bucketsMetadataPath); err != nil {
 		return err.Trace()
 	}
 	return nil
@@ -95,10 +60,6 @@ func saveBucketsMetadata(buckets *Buckets) *probe.Error {
 
 // loadMultipartsSession load multipart session file
 func loadMultipartsSession() (*Multiparts, *probe.Error) {
-	fsMultipartsConfigPath, err := getFSMultipartsSessionConfigPath()
-	if err != nil {
-		return nil, err.Trace()
-	}
 	multiparts := &Multiparts{}
 	multiparts.Version = "1"
 	multiparts.ActiveSession = make(map[string]*MultipartSession)
@@ -106,7 +67,7 @@ func loadMultipartsSession() (*Multiparts, *probe.Error) {
 	if err != nil {
 		return nil, err.Trace()
 	}
-	if err := qc.Load(fsMultipartsConfigPath); err != nil {
+	if err := qc.Load(multipartsMetadataPath); err != nil {
 		return nil, err.Trace()
 	}
 	return qc.Data().(*Multiparts), nil
@@ -114,10 +75,6 @@ func loadMultipartsSession() (*Multiparts, *probe.Error) {
 
 // loadBucketsMetadata load buckets metadata file
 func loadBucketsMetadata() (*Buckets, *probe.Error) {
-	fsBucketsConfigPath, err := getFSBucketsConfigPath()
-	if err != nil {
-		return nil, err.Trace()
-	}
 	buckets := &Buckets{}
 	buckets.Version = "1"
 	buckets.Metadata = make(map[string]*BucketMetadata)
@@ -125,7 +82,7 @@ func loadBucketsMetadata() (*Buckets, *probe.Error) {
 	if err != nil {
 		return nil, err.Trace()
 	}
-	if err := qc.Load(fsBucketsConfigPath); err != nil {
+	if err := qc.Load(bucketsMetadataPath); err != nil {
 		return nil, err.Trace()
 	}
 	return qc.Data().(*Buckets), nil
diff --git a/pkg/fs/definitions.go b/pkg/fs/definitions.go
index 96c31a4ef..a6d8d036b 100644
--- a/pkg/fs/definitions.go
+++ b/pkg/fs/definitions.go
@@ -68,7 +68,7 @@ type ObjectMetadata struct {
 	ContentType string
 	Created     time.Time
 	Mode        os.FileMode
-	Md5         string
+	MD5         string
 	Size        int64
 }
 
diff --git a/pkg/fs/errors.go b/pkg/fs/errors.go
index e6f27ad88..df81424d1 100644
--- a/pkg/fs/errors.go
+++ b/pkg/fs/errors.go
@@ -157,7 +157,7 @@ func (e InvalidDisksArgument) Error() string {
 
 // BadDigest bad md5sum
 type BadDigest struct {
-	Md5    string
+	MD5    string
 	Bucket string
 	Object string
 }
@@ -222,11 +222,11 @@ type ImplementationError struct {
 	Err    error
 }
 
-// DigestError - Generic Md5 error
+// DigestError - Generic MD5 error
 type DigestError struct {
 	Bucket string
 	Key    string
-	Md5    string
+	MD5    string
 }
 
 /// ACL related errors
@@ -322,7 +322,7 @@ func (e BackendCorrupted) Error() string {
 
 // Return string an error formatted as the given text
 func (e InvalidDigest) Error() string {
-	return "Md5 provided " + e.Md5 + " is invalid"
+	return "MD5 provided " + e.MD5 + " is invalid"
 }
 
 // OperationNotPermitted - operation not permitted
diff --git a/pkg/fs/fs-bucket-listobjects.go b/pkg/fs/fs-bucket-listobjects.go
index 8269d0fb8..cc9121f57 100644
--- a/pkg/fs/fs-bucket-listobjects.go
+++ b/pkg/fs/fs-bucket-listobjects.go
@@ -78,7 +78,13 @@ func (fs Filesystem) listObjects(bucket, prefix, marker, delimiter string, maxKe
 				walkPath = prefixPath
 			}
 		}
-		ioutils.FTW(walkPath, func(path string, info os.FileInfo, err error) error {
+		ioutils.FTW(walkPath, func(path string, info os.FileInfo, e error) error {
+			if e != nil {
+				return e
+			}
+			if strings.HasSuffix(path, "$multiparts") {
+				return nil
+			}
 			// We don't need to list the walk path.
 			if path == walkPath {
 				return nil
@@ -271,9 +277,6 @@ func (fs *Filesystem) listObjectsService() *probe.Error {
 // ListObjects - lists all objects for a given prefix, returns upto
 // maxKeys number of objects per call.
 func (fs Filesystem) ListObjects(bucket, prefix, marker, delimiter string, maxKeys int) (ListObjectsResult, *probe.Error) {
-	fs.rwLock.RLock()
-	defer fs.rwLock.RUnlock()
-
 	// Input validation.
 	if !IsValidBucketName(bucket) {
 		return ListObjectsResult{}, probe.NewError(BucketNameInvalid{Bucket: bucket})
diff --git a/pkg/fs/fs-bucket.go b/pkg/fs/fs-bucket.go
index 1352026d3..a39aac11a 100644
--- a/pkg/fs/fs-bucket.go
+++ b/pkg/fs/fs-bucket.go
@@ -32,8 +32,6 @@ import (
 
 // DeleteBucket - delete bucket
 func (fs Filesystem) DeleteBucket(bucket string) *probe.Error {
-	fs.rwLock.Lock()
-	defer fs.rwLock.Unlock()
 	// verify bucket path legal
 	if !IsValidBucketName(bucket) {
 		return probe.NewError(BucketNameInvalid{Bucket: bucket})
@@ -59,8 +57,10 @@ func (fs Filesystem) DeleteBucket(bucket string) *probe.Error {
 		}
 		return probe.NewError(e)
 	}
+	fs.rwLock.Lock()
 	delete(fs.buckets.Metadata, bucket)
-	if err := saveBucketsMetadata(fs.buckets); err != nil {
+	fs.rwLock.Unlock()
+	if err := saveBucketsMetadata(*fs.buckets); err != nil {
 		return err.Trace(bucket)
 	}
 	return nil
@@ -68,9 +68,6 @@ func (fs Filesystem) DeleteBucket(bucket string) *probe.Error {
 
 // ListBuckets - Get service.
 func (fs Filesystem) ListBuckets() ([]BucketMetadata, *probe.Error) {
-	fs.rwLock.RLock()
-	defer fs.rwLock.RUnlock()
-
 	files, err := ioutils.ReadDirN(fs.path, fs.maxBuckets)
 	if err != nil && err != io.EOF {
 		return []BucketMetadata{}, probe.NewError(err)
@@ -118,9 +115,6 @@ func removeDuplicateBuckets(elements []BucketMetadata) (result []BucketMetadata)
 
 // MakeBucket - PUT Bucket.
 func (fs Filesystem) MakeBucket(bucket, acl string) *probe.Error {
-	fs.rwLock.Lock()
-	defer fs.rwLock.Unlock()
-
 	di, err := disk.GetInfo(fs.path)
 	if err != nil {
 		return probe.NewError(err)
@@ -171,8 +165,10 @@ func (fs Filesystem) MakeBucket(bucket, acl string) *probe.Error {
 	bucketMetadata.Name = fi.Name()
 	bucketMetadata.Created = fi.ModTime()
 	bucketMetadata.ACL = BucketACL(acl)
+	fs.rwLock.Lock()
 	fs.buckets.Metadata[bucket] = bucketMetadata
-	if err := saveBucketsMetadata(fs.buckets); err != nil {
+	fs.rwLock.Unlock()
+	if err := saveBucketsMetadata(*fs.buckets); err != nil {
 		return err.Trace(bucket)
 	}
 	return nil
@@ -198,8 +194,6 @@ func (fs Filesystem) denormalizeBucket(bucket string) string {
 
 // GetBucketMetadata - get bucket metadata.
 func (fs Filesystem) GetBucketMetadata(bucket string) (BucketMetadata, *probe.Error) {
-	fs.rwLock.RLock()
-	defer fs.rwLock.RUnlock()
 	if !IsValidBucketName(bucket) {
 		return BucketMetadata{}, probe.NewError(BucketNameInvalid{Bucket: bucket})
 	}
@@ -215,7 +209,9 @@ func (fs Filesystem) GetBucketMetadata(bucket string) (BucketMetadata, *probe.Er
 		}
 		return BucketMetadata{}, probe.NewError(e)
 	}
+	fs.rwLock.RLock()
 	bucketMetadata, ok := fs.buckets.Metadata[bucket]
+	fs.rwLock.RUnlock()
 	if !ok {
 		bucketMetadata = &BucketMetadata{}
 		bucketMetadata.Name = fi.Name()
@@ -258,8 +254,10 @@ func (fs Filesystem) SetBucketMetadata(bucket string, metadata map[string]string
 		bucketMetadata.Created = fi.ModTime()
 	}
 	bucketMetadata.ACL = BucketACL(acl)
+	fs.rwLock.Lock()
 	fs.buckets.Metadata[bucket] = bucketMetadata
-	if err := saveBucketsMetadata(fs.buckets); err != nil {
+	fs.rwLock.Unlock()
+	if err := saveBucketsMetadata(*fs.buckets); err != nil {
 		return err.Trace(bucket)
 	}
 	return nil
diff --git a/pkg/fs/fs-common.go b/pkg/fs/fs-common.go
index 172cf23f0..71d2d53a1 100644
--- a/pkg/fs/fs-common.go
+++ b/pkg/fs/fs-common.go
@@ -27,7 +27,7 @@ import (
 
 // Metadata - carries metadata about object
 type Metadata struct {
-	Md5sum      []byte
+	MD5sum      []byte
 	ContentType string
 }
 
diff --git a/pkg/fs/fs-multipart.go b/pkg/fs/fs-multipart.go
index 997c7d01f..12446dfc2 100644
--- a/pkg/fs/fs-multipart.go
+++ b/pkg/fs/fs-multipart.go
@@ -44,6 +44,8 @@ import (
 
 // isValidUploadID - is upload id.
 func (fs Filesystem) isValidUploadID(object, uploadID string) bool {
+	fs.rwLock.RLock()
+	defer fs.rwLock.RUnlock()
 	s, ok := fs.multiparts.ActiveSession[object]
 	if !ok {
 		return false
@@ -56,9 +58,6 @@ func (fs Filesystem) isValidUploadID(object, uploadID string) bool {
 
 // ListMultipartUploads - list incomplete multipart sessions for a given BucketMultipartResourcesMetadata
 func (fs Filesystem) ListMultipartUploads(bucket string, resources BucketMultipartResourcesMetadata) (BucketMultipartResourcesMetadata, *probe.Error) {
-	fs.rwLock.RLock()
-	defer fs.rwLock.RUnlock()
-
 	// Input validation.
 	if !IsValidBucketName(bucket) {
 		return BucketMultipartResourcesMetadata{}, probe.NewError(BucketNameInvalid{Bucket: bucket})
@@ -73,6 +72,8 @@ func (fs Filesystem) ListMultipartUploads(bucket string, resources BucketMultipa
 		return BucketMultipartResourcesMetadata{}, probe.NewError(e)
 	}
 	var uploads []*UploadMetadata
+	fs.rwLock.RLock()
+	defer fs.rwLock.RUnlock()
 	for object, session := range fs.multiparts.ActiveSession {
 		if strings.HasPrefix(object, resources.Prefix) {
 			if len(uploads) > resources.MaxUploads {
@@ -117,34 +118,81 @@ func (fs Filesystem) ListMultipartUploads(bucket string, resources BucketMultipa
 	return resources, nil
 }
 
-// concatenate parts.
-func (fs Filesystem) concatParts(parts *CompleteMultipartUpload, objectPath string, mw io.Writer) *probe.Error {
-	for _, part := range parts.Part {
-		partFile, e := os.OpenFile(objectPath+fmt.Sprintf("$%d-$multiparts", part.PartNumber), os.O_RDONLY, 0600)
-		defer partFile.Close()
-		if e != nil {
-			return probe.NewError(e)
+// verify if parts sent over the network do really match with what we
+// have for the session.
+func doPartsMatch(parts []CompletePart, savedParts []*PartMetadata) bool {
+	if parts == nil || savedParts == nil {
+		return false
+	}
+	// Range of incoming parts and compare them with saved parts.
+	for i, part := range parts {
+		if strings.Trim(part.ETag, "\"") != savedParts[i].ETag {
+			return false
 		}
+	}
+	return true
+}
+
+type multiCloser struct {
+	Closers []io.Closer
+}
+
+func (m multiCloser) Close() error {
+	for _, c := range m.Closers {
+		if e := c.Close(); e != nil {
+			return e
+		}
+	}
+	return nil
+}
+
+// MultiCloser - returns a Closer that's the logical
+// concatenation of the provided input closers. They're closed
+// sequentially. If any of the closers return a non-nil error, Close
+// will return that error.
+func MultiCloser(closers ...io.Closer) io.Closer {
+	return multiCloser{closers}
+}
 
-		recvMD5 := part.ETag
-		// Complete multipart request header md5sum per part is hex
-		// encoded trim it and decode if possible.
-		if _, e = hex.DecodeString(strings.Trim(recvMD5, "\"")); e != nil {
-			return probe.NewError(InvalidDigest{Md5: recvMD5})
+// removeParts - remove all parts.
+func removeParts(partPathPrefix string, parts []*PartMetadata) *probe.Error {
+	for _, part := range parts {
+		if e := os.Remove(partPathPrefix + fmt.Sprintf("$%d-$multiparts", part.PartNumber)); e != nil {
+			return probe.NewError(e)
 		}
+	}
+	if e := os.Remove(partPathPrefix + "$multiparts"); e != nil {
+		return probe.NewError(e)
+	}
+	return nil
+}
 
-		if _, e = io.Copy(mw, partFile); e != nil {
+// saveParts - concantenate and save all parts.
+func saveParts(partPathPrefix string, mw io.Writer, parts []CompletePart) *probe.Error {
+	var partReaders []io.Reader
+	var partClosers []io.Closer
+	for _, part := range parts {
+		partFile, e := os.OpenFile(partPathPrefix+fmt.Sprintf("$%d-$multiparts", part.PartNumber), os.O_RDONLY, 0600)
+		if e != nil {
 			return probe.NewError(e)
 		}
+		partReaders = append(partReaders, partFile)
+		partClosers = append(partClosers, partFile)
+	}
+	// Concatenate a list of closers and close upon return.
+	closer := MultiCloser(partClosers...)
+	defer closer.Close()
+
+	reader := io.MultiReader(partReaders...)
+	readBuffer := make([]byte, 4*1024*1024)
+	if _, e := io.CopyBuffer(mw, reader, readBuffer); e != nil {
+		return probe.NewError(e)
 	}
 	return nil
 }
 
 // NewMultipartUpload - initiate a new multipart session
 func (fs Filesystem) NewMultipartUpload(bucket, object string) (string, *probe.Error) {
-	fs.rwLock.Lock()
-	defer fs.rwLock.Unlock()
-
 	di, e := disk.GetInfo(fs.path)
 	if e != nil {
 		return "", probe.NewError(e)
@@ -192,12 +240,6 @@ func (fs Filesystem) NewMultipartUpload(bucket, object string) (string, *probe.E
 	uploadIDSum := sha512.Sum512(id)
 	uploadID := base64.URLEncoding.EncodeToString(uploadIDSum[:])[:47]
 
-	multiPartfile, e := os.OpenFile(objectPath+"$multiparts", os.O_WRONLY|os.O_CREATE, 0600)
-	if e != nil {
-		return "", probe.NewError(e)
-	}
-	defer multiPartfile.Close()
-
 	// Initialize multipart session.
 	mpartSession := &MultipartSession{}
 	mpartSession.TotalParts = 0
@@ -205,14 +247,23 @@ func (fs Filesystem) NewMultipartUpload(bucket, object string) (string, *probe.E
 	mpartSession.Initiated = time.Now().UTC()
 	var parts []*PartMetadata
 	mpartSession.Parts = parts
+
+	fs.rwLock.Lock()
 	fs.multiparts.ActiveSession[object] = mpartSession
+	fs.rwLock.Unlock()
+
+	mpartSessionBytes, e := json.Marshal(mpartSession)
+	if e != nil {
+		return "", probe.NewError(e)
+	}
 
-	encoder := json.NewEncoder(multiPartfile)
-	if e = encoder.Encode(mpartSession); e != nil {
+	partPathPrefix := objectPath + uploadID
+	if e = ioutil.WriteFile(partPathPrefix+"$multiparts", mpartSessionBytes, 0600); e != nil {
 		return "", probe.NewError(e)
 	}
-	if err := saveMultipartsSession(fs.multiparts); err != nil {
-		return "", err.Trace()
+
+	if err := saveMultipartsSession(*fs.multiparts); err != nil {
+		return "", err.Trace(partPathPrefix)
 	}
 	return uploadID, nil
 }
@@ -226,9 +277,6 @@ func (a partNumber) Less(i, j int) bool { return a[i].PartNumber < a[j].PartNumb
 
 // CreateObjectPart - create a part in a multipart session
 func (fs Filesystem) CreateObjectPart(bucket, object, uploadID, expectedMD5Sum string, partID int, size int64, data io.Reader, signature *Signature) (string, *probe.Error) {
-	fs.rwLock.Lock()
-	defer fs.rwLock.Unlock()
-
 	di, err := disk.GetInfo(fs.path)
 	if err != nil {
 		return "", probe.NewError(err)
@@ -266,7 +314,7 @@ func (fs Filesystem) CreateObjectPart(bucket, object, uploadID, expectedMD5Sum s
 		expectedMD5SumBytes, err = base64.StdEncoding.DecodeString(strings.TrimSpace(expectedMD5Sum))
 		if err != nil {
 			// Pro-actively close the connection
-			return "", probe.NewError(InvalidDigest{Md5: expectedMD5Sum})
+			return "", probe.NewError(InvalidDigest{MD5: expectedMD5Sum})
 		}
 		expectedMD5Sum = hex.EncodeToString(expectedMD5SumBytes)
 	}
@@ -282,29 +330,32 @@ func (fs Filesystem) CreateObjectPart(bucket, object, uploadID, expectedMD5Sum s
 	}
 
 	objectPath := filepath.Join(bucketPath, object)
-	partPath := objectPath + fmt.Sprintf("$%d-$multiparts", partID)
+	partPathPrefix := objectPath + uploadID
+	partPath := partPathPrefix + fmt.Sprintf("$%d-$multiparts", partID)
 	partFile, e := atomic.FileCreateWithPrefix(partPath, "$multiparts")
 	if e != nil {
 		return "", probe.NewError(e)
 	}
-	h := md5.New()
-	sh := sha256.New()
-	mw := io.MultiWriter(partFile, h, sh)
-	if _, e = io.CopyN(mw, data, size); e != nil {
+
+	md5Hasher := md5.New()
+	sha256Hasher := sha256.New()
+	partWriter := io.MultiWriter(partFile, md5Hasher, sha256Hasher)
+	if _, e = io.CopyN(partWriter, data, size); e != nil {
 		partFile.CloseAndPurge()
 		return "", probe.NewError(e)
 	}
-	md5sum := hex.EncodeToString(h.Sum(nil))
+
+	md5sum := hex.EncodeToString(md5Hasher.Sum(nil))
 	// Verify if the written object is equal to what is expected, only
 	// if it is requested as such.
 	if strings.TrimSpace(expectedMD5Sum) != "" {
 		if !isMD5SumEqual(strings.TrimSpace(expectedMD5Sum), md5sum) {
 			partFile.CloseAndPurge()
-			return "", probe.NewError(BadDigest{Md5: expectedMD5Sum, Bucket: bucket, Object: object})
+			return "", probe.NewError(BadDigest{MD5: expectedMD5Sum, Bucket: bucket, Object: object})
 		}
 	}
 	if signature != nil {
-		ok, err := signature.DoesSignatureMatch(hex.EncodeToString(sh.Sum(nil)))
+		ok, err := signature.DoesSignatureMatch(hex.EncodeToString(sha256Hasher.Sum(nil)))
 		if err != nil {
 			partFile.CloseAndPurge()
 			return "", err.Trace()
@@ -326,24 +377,30 @@ func (fs Filesystem) CreateObjectPart(bucket, object, uploadID, expectedMD5Sum s
 	partMetadata.Size = fi.Size()
 	partMetadata.LastModified = fi.ModTime()
 
-	multiPartfile, e := os.OpenFile(objectPath+"$multiparts", os.O_RDWR|os.O_APPEND, 0600)
+	multipartSessionBytes, e := ioutil.ReadFile(partPathPrefix + "$multiparts")
 	if e != nil {
 		return "", probe.NewError(e)
 	}
-	defer multiPartfile.Close()
 
 	var deserializedMultipartSession MultipartSession
-	decoder := json.NewDecoder(multiPartfile)
-	if e = decoder.Decode(&deserializedMultipartSession); e != nil {
+	if e = json.Unmarshal(multipartSessionBytes, &deserializedMultipartSession); e != nil {
 		return "", probe.NewError(e)
 	}
 	deserializedMultipartSession.Parts = append(deserializedMultipartSession.Parts, &partMetadata)
 	deserializedMultipartSession.TotalParts++
+
+	fs.rwLock.Lock()
 	fs.multiparts.ActiveSession[object] = &deserializedMultipartSession
+	fs.rwLock.Unlock()
 
+	// Sort by part number before saving.
 	sort.Sort(partNumber(deserializedMultipartSession.Parts))
-	encoder := json.NewEncoder(multiPartfile)
-	if e = encoder.Encode(&deserializedMultipartSession); e != nil {
+
+	multipartSessionBytes, e = json.Marshal(deserializedMultipartSession)
+	if e != nil {
+		return "", probe.NewError(e)
+	}
+	if e = ioutil.WriteFile(partPathPrefix+"$multiparts", multipartSessionBytes, 0600); e != nil {
 		return "", probe.NewError(e)
 	}
 	return partMetadata.ETag, nil
@@ -351,9 +408,6 @@ func (fs Filesystem) CreateObjectPart(bucket, object, uploadID, expectedMD5Sum s
 
 // CompleteMultipartUpload - complete a multipart upload and persist the data
 func (fs Filesystem) CompleteMultipartUpload(bucket, object, uploadID string, data io.Reader, signature *Signature) (ObjectMetadata, *probe.Error) {
-	fs.rwLock.Lock()
-	defer fs.rwLock.Unlock()
-
 	// Check bucket name is valid.
 	if !IsValidBucketName(bucket) {
 		return ObjectMetadata{}, probe.NewError(BucketNameInvalid{Bucket: bucket})
@@ -384,8 +438,8 @@ func (fs Filesystem) CompleteMultipartUpload(bucket, object, uploadID string, da
 	if e != nil {
 		return ObjectMetadata{}, probe.NewError(e)
 	}
-	h := md5.New()
-	mw := io.MultiWriter(file, h)
+	md5Hasher := md5.New()
+	objectWriter := io.MultiWriter(file, md5Hasher)
 
 	partBytes, e := ioutil.ReadAll(data)
 	if e != nil {
@@ -405,35 +459,45 @@ func (fs Filesystem) CompleteMultipartUpload(bucket, object, uploadID string, da
 			return ObjectMetadata{}, probe.NewError(SignatureDoesNotMatch{})
 		}
 	}
-	parts := &CompleteMultipartUpload{}
-	if e := xml.Unmarshal(partBytes, parts); e != nil {
+	completeMultipartUpload := &CompleteMultipartUpload{}
+	if e := xml.Unmarshal(partBytes, completeMultipartUpload); e != nil {
 		file.CloseAndPurge()
 		return ObjectMetadata{}, probe.NewError(MalformedXML{})
 	}
-	if !sort.IsSorted(completedParts(parts.Part)) {
+	if !sort.IsSorted(completedParts(completeMultipartUpload.Part)) {
 		file.CloseAndPurge()
 		return ObjectMetadata{}, probe.NewError(InvalidPartOrder{})
 	}
 
-	if err := fs.concatParts(parts, objectPath, mw); err != nil {
+	// Save parts for verification.
+	parts := completeMultipartUpload.Part
+
+	fs.rwLock.RLock()
+	savedParts := fs.multiparts.ActiveSession[object].Parts
+	fs.rwLock.RUnlock()
+
+	if !doPartsMatch(parts, savedParts) {
 		file.CloseAndPurge()
-		return ObjectMetadata{}, err.Trace()
+		return ObjectMetadata{}, probe.NewError(InvalidPart{})
 	}
 
-	delete(fs.multiparts.ActiveSession, object)
-	for _, part := range parts.Part {
-		if e = os.Remove(objectPath + fmt.Sprintf("$%d-$multiparts", part.PartNumber)); e != nil {
-			file.CloseAndPurge()
-			return ObjectMetadata{}, probe.NewError(e)
-		}
+	partPathPrefix := objectPath + uploadID
+	if err := saveParts(partPathPrefix, objectWriter, parts); err != nil {
+		file.CloseAndPurge()
+		return ObjectMetadata{}, err.Trace(partPathPrefix)
 	}
-	if e := os.Remove(objectPath + "$multiparts"); e != nil {
+	if err := removeParts(partPathPrefix, savedParts); err != nil {
 		file.CloseAndPurge()
-		return ObjectMetadata{}, probe.NewError(e)
+		return ObjectMetadata{}, err.Trace(partPathPrefix)
 	}
-	if e := saveMultipartsSession(fs.multiparts); e != nil {
+
+	fs.rwLock.Lock()
+	delete(fs.multiparts.ActiveSession, object)
+	fs.rwLock.Unlock()
+
+	if err := saveMultipartsSession(*fs.multiparts); err != nil {
 		file.CloseAndPurge()
-		return ObjectMetadata{}, e.Trace()
+		return ObjectMetadata{}, err.Trace(partPathPrefix)
 	}
 	file.Close()
 
@@ -451,16 +515,13 @@ func (fs Filesystem) CompleteMultipartUpload(bucket, object, uploadID string, da
 		Created:     st.ModTime(),
 		Size:        st.Size(),
 		ContentType: contentType,
-		Md5:         hex.EncodeToString(h.Sum(nil)),
+		MD5:         hex.EncodeToString(md5Hasher.Sum(nil)),
 	}
 	return newObject, nil
 }
 
 // ListObjectParts - list parts from incomplete multipart session for a given ObjectResourcesMetadata
 func (fs Filesystem) ListObjectParts(bucket, object string, resources ObjectResourcesMetadata) (ObjectResourcesMetadata, *probe.Error) {
-	fs.rwLock.Lock()
-	defer fs.rwLock.Unlock()
-
 	// Check bucket name is valid.
 	if !IsValidBucketName(bucket) {
 		return ObjectResourcesMetadata{}, probe.NewError(BucketNameInvalid{Bucket: bucket})
@@ -498,17 +559,16 @@ func (fs Filesystem) ListObjectParts(bucket, object string, resources ObjectReso
 	}
 
 	objectPath := filepath.Join(bucketPath, object)
-	multiPartfile, e := os.OpenFile(objectPath+"$multiparts", os.O_RDONLY, 0600)
+	partPathPrefix := objectPath + resources.UploadID
+	multipartSessionBytes, e := ioutil.ReadFile(partPathPrefix + "$multiparts")
 	if e != nil {
 		return ObjectResourcesMetadata{}, probe.NewError(e)
 	}
-	defer multiPartfile.Close()
-
 	var deserializedMultipartSession MultipartSession
-	decoder := json.NewDecoder(multiPartfile)
-	if e = decoder.Decode(&deserializedMultipartSession); e != nil {
+	if e = json.Unmarshal(multipartSessionBytes, &deserializedMultipartSession); e != nil {
 		return ObjectResourcesMetadata{}, probe.NewError(e)
 	}
+
 	var parts []*PartMetadata
 	for i := startPartNumber; i <= deserializedMultipartSession.TotalParts; i++ {
 		if len(parts) > objectResourcesMetadata.MaxParts {
@@ -527,9 +587,6 @@ func (fs Filesystem) ListObjectParts(bucket, object string, resources ObjectReso
 
 // AbortMultipartUpload - abort an incomplete multipart session
 func (fs Filesystem) AbortMultipartUpload(bucket, object, uploadID string) *probe.Error {
-	fs.rwLock.Lock()
-	defer fs.rwLock.Unlock()
-
 	// Check bucket name valid.
 	if !IsValidBucketName(bucket) {
 		return probe.NewError(BucketNameInvalid{Bucket: bucket})
@@ -555,15 +612,20 @@ func (fs Filesystem) AbortMultipartUpload(bucket, object, uploadID string) *prob
 	}
 
 	objectPath := filepath.Join(bucketPath, object)
-	for _, part := range fs.multiparts.ActiveSession[object].Parts {
-		e := os.RemoveAll(objectPath + fmt.Sprintf("$%d-$multiparts", part.PartNumber))
-		if e != nil {
-			return probe.NewError(e)
-		}
+	partPathPrefix := objectPath + uploadID
+	fs.rwLock.RLock()
+	savedParts := fs.multiparts.ActiveSession[object].Parts
+	fs.rwLock.RUnlock()
+
+	if err := removeParts(partPathPrefix, savedParts); err != nil {
+		return err.Trace(partPathPrefix)
 	}
+
+	fs.rwLock.Lock()
 	delete(fs.multiparts.ActiveSession, object)
-	if e := os.RemoveAll(objectPath + "$multiparts"); e != nil {
-		return probe.NewError(e)
+	fs.rwLock.Unlock()
+	if err := saveMultipartsSession(*fs.multiparts); err != nil {
+		return err.Trace(partPathPrefix)
 	}
 	return nil
 }
diff --git a/pkg/fs/fs-object.go b/pkg/fs/fs-object.go
index c0082826c..87f5b3528 100644
--- a/pkg/fs/fs-object.go
+++ b/pkg/fs/fs-object.go
@@ -102,9 +102,6 @@ func (fs Filesystem) GetObject(w io.Writer, bucket, object string, start, length
 
 // GetObjectMetadata - get object metadata.
 func (fs Filesystem) GetObjectMetadata(bucket, object string) (ObjectMetadata, *probe.Error) {
-	fs.rwLock.RLock()
-	defer fs.rwLock.RUnlock()
-
 	// Input validation.
 	if !IsValidBucketName(bucket) {
 		return ObjectMetadata{}, probe.NewError(BucketNameInvalid{Bucket: bucket})
@@ -193,9 +190,6 @@ func isMD5SumEqual(expectedMD5Sum, actualMD5Sum string) bool {
 
 // CreateObject - create an object.
 func (fs Filesystem) CreateObject(bucket, object, expectedMD5Sum string, size int64, data io.Reader, signature *Signature) (ObjectMetadata, *probe.Error) {
-	fs.rwLock.Lock()
-	defer fs.rwLock.Unlock()
-
 	di, e := disk.GetInfo(fs.path)
 	if e != nil {
 		return ObjectMetadata{}, probe.NewError(e)
@@ -233,7 +227,7 @@ func (fs Filesystem) CreateObject(bucket, object, expectedMD5Sum string, size in
 		expectedMD5SumBytes, e = base64.StdEncoding.DecodeString(strings.TrimSpace(expectedMD5Sum))
 		if e != nil {
 			// Pro-actively close the connection.
-			return ObjectMetadata{}, probe.NewError(InvalidDigest{Md5: expectedMD5Sum})
+			return ObjectMetadata{}, probe.NewError(InvalidDigest{MD5: expectedMD5Sum})
 		}
 		expectedMD5Sum = hex.EncodeToString(expectedMD5SumBytes)
 	}
@@ -276,7 +270,7 @@ func (fs Filesystem) CreateObject(bucket, object, expectedMD5Sum string, size in
 	if strings.TrimSpace(expectedMD5Sum) != "" {
 		if !isMD5SumEqual(strings.TrimSpace(expectedMD5Sum), md5Sum) {
 			file.CloseAndPurge()
-			return ObjectMetadata{}, probe.NewError(BadDigest{Md5: expectedMD5Sum, Bucket: bucket, Object: object})
+			return ObjectMetadata{}, probe.NewError(BadDigest{MD5: expectedMD5Sum, Bucket: bucket, Object: object})
 		}
 	}
 	sha256Sum := hex.EncodeToString(sh.Sum(nil))
@@ -307,7 +301,7 @@ func (fs Filesystem) CreateObject(bucket, object, expectedMD5Sum string, size in
 		Created:     st.ModTime(),
 		Size:        st.Size(),
 		ContentType: contentType,
-		Md5:         md5Sum,
+		MD5:         md5Sum,
 	}
 	return newObject, nil
 }
@@ -344,9 +338,6 @@ func deleteObjectPath(basePath, deletePath, bucket, object string) *probe.Error
 
 // DeleteObject - delete and object
 func (fs Filesystem) DeleteObject(bucket, object string) *probe.Error {
-	fs.rwLock.Lock()
-	defer fs.rwLock.Unlock()
-
 	// check bucket name valid
 	if !IsValidBucketName(bucket) {
 		return probe.NewError(BucketNameInvalid{Bucket: bucket})
diff --git a/pkg/fs/fs.go b/pkg/fs/fs.go
index 1b685fa8c..ba4528a63 100644
--- a/pkg/fs/fs.go
+++ b/pkg/fs/fs.go
@@ -60,8 +60,8 @@ type Multiparts struct {
 
 // New instantiate a new donut
 func New(rootPath string, minFreeDisk int64, maxBuckets int) (Filesystem, *probe.Error) {
-	setFSBucketsConfigPath(filepath.Join(rootPath, "$buckets.json"))
-	setFSMultipartsConfigPath(filepath.Join(rootPath, "$multiparts-session.json"))
+	setFSBucketsMetadataPath(filepath.Join(rootPath, "$buckets.json"))
+	setFSMultipartsMetadataPath(filepath.Join(rootPath, "$multiparts-session.json"))
 
 	var err *probe.Error
 	// load multiparts session from disk
@@ -73,7 +73,7 @@ func New(rootPath string, minFreeDisk int64, maxBuckets int) (Filesystem, *probe
 				Version:       "1",
 				ActiveSession: make(map[string]*MultipartSession),
 			}
-			if err := saveMultipartsSession(multiparts); err != nil {
+			if err := saveMultipartsSession(*multiparts); err != nil {
 				return Filesystem{}, err.Trace()
 			}
 		} else {
@@ -94,7 +94,7 @@ func New(rootPath string, minFreeDisk int64, maxBuckets int) (Filesystem, *probe
 				Version:  "1",
 				Metadata: make(map[string]*BucketMetadata),
 			}
-			if err := saveBucketsMetadata(buckets); err != nil {
+			if err := saveBucketsMetadata(*buckets); err != nil {
 				return Filesystem{}, err.Trace()
 			}
 		} else {