diff --git a/pkg/donut/donut-v2.go b/pkg/donut/donut-v2.go
index 4a81e9ebf..bcb0997c2 100644
--- a/pkg/donut/donut-v2.go
+++ b/pkg/donut/donut-v2.go
@@ -67,7 +67,7 @@ type API struct {
 type storedBucket struct {
 	bucketMetadata   BucketMetadata
 	objectMetadata   map[string]ObjectMetadata
-	partMetadata     map[int]PartMetadata
+	partMetadata     map[string]map[int]PartMetadata
 	multiPartSession map[string]MultiPartSession
 }
 
@@ -116,7 +116,7 @@ func New() (Interface, error) {
 			newBucket.bucketMetadata = v
 			newBucket.objectMetadata = make(map[string]ObjectMetadata)
 			newBucket.multiPartSession = make(map[string]MultiPartSession)
-			newBucket.partMetadata = make(map[int]PartMetadata)
+			newBucket.partMetadata = make(map[string]map[int]PartMetadata)
 			a.storedBuckets.Set(k, newBucket)
 		}
 	}
@@ -487,7 +487,7 @@ func (donut API) MakeBucket(bucketName, acl string, signature *Signature) error
 	var newBucket = storedBucket{}
 	newBucket.objectMetadata = make(map[string]ObjectMetadata)
 	newBucket.multiPartSession = make(map[string]MultiPartSession)
-	newBucket.partMetadata = make(map[int]PartMetadata)
+	newBucket.partMetadata = make(map[string]map[int]PartMetadata)
 	newBucket.bucketMetadata = BucketMetadata{}
 	newBucket.bucketMetadata.Name = bucketName
 	newBucket.bucketMetadata.Created = time.Now().UTC()
diff --git a/pkg/donut/multipart.go b/pkg/donut/multipart.go
index 901133eed..48e23fba8 100644
--- a/pkg/donut/multipart.go
+++ b/pkg/donut/multipart.go
@@ -23,7 +23,6 @@ import (
 	"encoding/base64"
 	"encoding/hex"
 	"encoding/xml"
-	"errors"
 	"io"
 	"io/ioutil"
 	"math/rand"
@@ -78,6 +77,7 @@ func (donut API) NewMultipartUpload(bucket, key, contentType string, signature *
 		initiated:  time.Now(),
 		totalParts: 0,
 	}
+	storedBucket.partMetadata[key] = make(map[int]PartMetadata)
 	multiPartCache := data.NewCache(0)
 	multiPartCache.OnEvicted = donut.evictedPart
 	donut.multiPartObjects[uploadID] = multiPartCache
@@ -117,9 +117,8 @@ func (donut API) AbortMultipartUpload(bucket, key, uploadID string, signature *S
 // CreateObjectPart - create a part in a multipart session
 func (donut API) CreateObjectPart(bucket, key, uploadID string, partID int, contentType, expectedMD5Sum string, size int64, data io.Reader, signature *Signature) (string, error) {
 	donut.lock.Lock()
-	defer donut.lock.Unlock()
-
 	etag, err := donut.createObjectPart(bucket, key, uploadID, partID, "", expectedMD5Sum, size, data, signature)
+	donut.lock.Unlock()
 	// possible free
 	debug.FreeOSMemory()
 
@@ -137,15 +136,16 @@ func (donut API) createObjectPart(bucket, key, uploadID string, partID int, cont
 	if !donut.storedBuckets.Exists(bucket) {
 		return "", iodine.New(BucketNotFound{Bucket: bucket}, nil)
 	}
-	storedBucket := donut.storedBuckets.Get(bucket).(storedBucket)
+	strBucket := donut.storedBuckets.Get(bucket).(storedBucket)
 	// Verify upload id
-	if storedBucket.multiPartSession[key].uploadID != uploadID {
+	if strBucket.multiPartSession[key].uploadID != uploadID {
 		return "", iodine.New(InvalidUploadID{UploadID: uploadID}, nil)
 	}
 
 	// get object key
-	if _, ok := storedBucket.partMetadata[partID]; ok {
-		return storedBucket.partMetadata[partID].ETag, nil
+	parts := strBucket.partMetadata[key]
+	if _, ok := parts[partID]; ok {
+		return parts[partID].ETag, nil
 	}
 
 	if contentType == "" {
@@ -214,11 +214,12 @@ func (donut API) createObjectPart(bucket, key, uploadID string, partID int, cont
 		Size:         totalLength,
 	}
 
-	storedBucket.partMetadata[partID] = newPart
-	multiPartSession := storedBucket.multiPartSession[key]
+	parts[partID] = newPart
+	strBucket.partMetadata[key] = parts
+	multiPartSession := strBucket.multiPartSession[key]
 	multiPartSession.totalParts++
-	storedBucket.multiPartSession[key] = multiPartSession
-	donut.storedBuckets.Set(bucket, storedBucket)
+	strBucket.multiPartSession[key] = multiPartSession
+	donut.storedBuckets.Set(bucket, strBucket)
 	return md5Sum, nil
 }
 
@@ -229,6 +230,7 @@ func (donut API) cleanupMultipartSession(bucket, key, uploadID string) {
 		donut.multiPartObjects[uploadID].Delete(i)
 	}
 	delete(storedBucket.multiPartSession, key)
+	delete(storedBucket.partMetadata, key)
 	donut.storedBuckets.Set(bucket, storedBucket)
 }
 
@@ -279,6 +281,7 @@ func (donut API) CompleteMultipartUpload(bucket, key, uploadID string, data io.R
 		donut.lock.Unlock()
 		return ObjectMetadata{}, iodine.New(InvalidPartOrder{}, nil)
 	}
+
 	var size int64
 	var fullObject bytes.Buffer
 	for i := 0; i < len(parts.Part); i++ {
@@ -434,6 +437,7 @@ func (donut API) ListObjectParts(bucket, key string, resources ObjectResourcesMe
 	if storedBucket.multiPartSession[key].uploadID != resources.UploadID {
 		return ObjectResourcesMetadata{}, iodine.New(InvalidUploadID{UploadID: resources.UploadID}, nil)
 	}
+	storedParts := storedBucket.partMetadata[key]
 	objectResourcesMetadata := resources
 	objectResourcesMetadata.Bucket = bucket
 	objectResourcesMetadata.Key = key
@@ -453,9 +457,9 @@ func (donut API) ListObjectParts(bucket, key string, resources ObjectResourcesMe
 			objectResourcesMetadata.NextPartNumberMarker = i
 			return objectResourcesMetadata, nil
 		}
-		part, ok := storedBucket.partMetadata[i]
+		part, ok := storedParts[i]
 		if !ok {
-			return ObjectResourcesMetadata{}, iodine.New(errors.New("missing part: "+strconv.Itoa(i)), nil)
+			return ObjectResourcesMetadata{}, iodine.New(InvalidPart{}, nil)
 		}
 		parts = append(parts, &part)
 	}
@@ -466,12 +470,10 @@ func (donut API) ListObjectParts(bucket, key string, resources ObjectResourcesMe
 
 // evictedPart - call back function called by caching module during individual cache evictions
 func (donut API) evictedPart(a ...interface{}) {
-	key := a[0].(int)
 	// loop through all buckets
 	buckets := donut.storedBuckets.GetAll()
 	for bucketName, bucket := range buckets {
 		b := bucket.(storedBucket)
-		delete(b.partMetadata, key)
 		donut.storedBuckets.Set(bucketName, b)
 	}
 	debug.FreeOSMemory()