// instead of "copying" from source, we need the stream to be seekable
		// to ensure that we can make fan-out calls concurrently.
		buf := bytebufferpool.Get()
		defer func() {
			buf.Reset()
			bytebufferpool.Put(buf)
		}()

		md5w := md5.New()

		// Maximum allowed fan-out object size.
		const maxFanOutSize = 16 << 20