diff --git a/cmd/api-errors.go b/cmd/api-errors.go
index cac9cb22d..8b7d7b06d 100644
--- a/cmd/api-errors.go
+++ b/cmd/api-errors.go
@@ -1082,9 +1082,9 @@ var errorCodes = errorCodeMap{
 		HTTPStatusCode: http.StatusBadRequest,
 	},
 	ErrKMSNotConfigured: {
-		Code:           "InvalidArgument",
+		Code:           "NotImplemented",
 		Description:    "Server side encryption specified but KMS is not configured",
-		HTTPStatusCode: http.StatusBadRequest,
+		HTTPStatusCode: http.StatusNotImplemented,
 	},
 	ErrNoAccessKey: {
 		Code:           "AccessDenied",
diff --git a/cmd/erasure-server-pool.go b/cmd/erasure-server-pool.go
index 9e900c8c7..53b394d20 100644
--- a/cmd/erasure-server-pool.go
+++ b/cmd/erasure-server-pool.go
@@ -268,47 +268,6 @@ func (z *erasureServerPools) getPoolIdxExisting(ctx context.Context, bucket, obj
 	}
 	wg.Wait()
 
-	for i, err := range errs {
-		if err == nil {
-			return i, nil
-		}
-		if isErrObjectNotFound(err) {
-			// No object exists or its a delete marker,
-			// check objInfo to confirm.
-			if objInfos[i].DeleteMarker && objInfos[i].Name != "" {
-				return i, nil
-			}
-
-			// objInfo is not valid, truly the object doesn't
-			// exist proceed to next pool.
-			continue
-		}
-		return -1, err
-	}
-
-	return -1, toObjectErr(errFileNotFound, bucket, object)
-}
-
-// getPoolIdx returns the found previous object and its corresponding pool idx,
-// if none are found falls back to most available space pool.
-func (z *erasureServerPools) getPoolIdx(ctx context.Context, bucket, object string, size int64) (idx int, err error) {
-	if z.SinglePool() {
-		return 0, nil
-	}
-
-	errs := make([]error, len(z.serverPools))
-	objInfos := make([]ObjectInfo, len(z.serverPools))
-
-	var wg sync.WaitGroup
-	for i, pool := range z.serverPools {
-		wg.Add(1)
-		go func(i int, pool *erasureSets) {
-			defer wg.Done()
-			objInfos[i], errs[i] = pool.GetObjectInfo(ctx, bucket, object, ObjectOptions{})
-		}(i, pool)
-	}
-	wg.Wait()
-
 	for i, err := range errs {
 		if err != nil && !isErrObjectNotFound(err) {
 			return -1, err
@@ -319,19 +278,33 @@ func (z *erasureServerPools) getPoolIdx(ctx context.Context, bucket, object stri
 			if objInfos[i].DeleteMarker && objInfos[i].Name != "" {
 				return i, nil
 			}
+
 			// objInfo is not valid, truly the object doesn't
 			// exist proceed to next pool.
 			continue
 		}
-		// object exists at this pool.
 		return i, nil
 	}
 
-	// We multiply the size by 2 to account for erasure coding.
-	idx = z.getAvailablePoolIdx(ctx, size*2)
-	if idx < 0 {
-		return -1, toObjectErr(errDiskFull)
+	return -1, toObjectErr(errFileNotFound, bucket, object)
+}
+
+// getPoolIdx returns the found previous object and its corresponding pool idx,
+// if none are found falls back to most available space pool.
+func (z *erasureServerPools) getPoolIdx(ctx context.Context, bucket, object string, size int64) (idx int, err error) {
+	idx, err = z.getPoolIdxExisting(ctx, bucket, object)
+	if err != nil && !isErrObjectNotFound(err) {
+		return idx, err
 	}
+
+	if isErrObjectNotFound(err) {
+		// We multiply the size by 2 to account for erasure coding.
+		idx = z.getAvailablePoolIdx(ctx, size*2)
+		if idx < 0 {
+			return -1, toObjectErr(errDiskFull)
+		}
+	}
+
 	return idx, nil
 }
 
@@ -1039,6 +1012,14 @@ func (z *erasureServerPools) NewMultipartUpload(ctx context.Context, bucket, obj
 		return z.serverPools[0].NewMultipartUpload(ctx, bucket, object, opts)
 	}
 
+	ns := z.NewNSLock(minioMetaMultipartBucket, pathJoin(bucket, object, "newMultipartObject.lck"))
+	lkctx, err := ns.GetLock(ctx, globalOperationTimeout)
+	if err != nil {
+		return "", err
+	}
+	ctx = lkctx.Context()
+	defer ns.Unlock(lkctx.Cancel)
+
 	for idx, pool := range z.serverPools {
 		result, err := pool.ListMultipartUploads(ctx, bucket, object, "", "", "", maxUploadsList)
 		if err != nil {
@@ -1052,10 +1033,9 @@ func (z *erasureServerPools) NewMultipartUpload(ctx context.Context, bucket, obj
 		}
 	}
 
-	// We multiply the size by 2 to account for erasure coding.
-	idx := z.getAvailablePoolIdx(ctx, (1<<30)*2)
-	if idx < 0 {
-		return "", toObjectErr(errDiskFull)
+	idx, err := z.getPoolIdx(ctx, bucket, object, 1<<30)
+	if err != nil {
+		return "", err
 	}
 
 	return z.serverPools[idx].NewMultipartUpload(ctx, bucket, object, opts)