Described herein are technologies directed to multipart upload. A cluster coherent unique identifier for a multipart upload can be generated by creating a leaf in a B-tree. The leaf in the B-tree can comprise a key, and the key can comprise an upload identifier and a group identifier associated with a group of multipart uploads. A parts directory can be created for the multipart upload, wherein elements of the parts directory can be identified using the group identifier and the upload identifier. Upload parts can be transmitted from a client device to a server device, and stored in the parts directory. To complete the multipart upload, the upload parts can be concatenated and stored at a target location.