startOffset, length, err := rs.GetOffsetLength(actualPartSize)
	if err != nil {
		writeErrorResponse(ctx, w, toAPIError(ctx, err), r.URL)
		return
	}

	// maximum copy size for multipart objects in a single operation
	if isMaxObjectSize(length) {
		writeErrorResponse(ctx, w, errorCodes.ToAPIErr(ErrEntityTooLarge), r.URL)
		return
	}

	if isRemoteCopyRequired(ctx, srcBucket, dstBucket, objectAPI) {

		reqInfo.ObjectName = srcObject
		writeErrorResponse(ctx, w, toAPIError(ctx, err), r.URL)
		return
	}
	defer gr.Close()
	srcInfo := gr.ObjInfo

	// maximum Upload size for object in a single CopyObject operation.
	if isMaxObjectSize(srcInfo.Size) {
		writeErrorResponse(ctx, w, errorCodes.ToAPIErr(ErrEntityTooLarge), r.URL)
		return
	}

	// otherwise return failure. Cleanup successful renames.
	return evalDisks(disks, errs), err
}

// PutObjectPart - reads incoming stream and internally erasure codes
// them. This call is similar to single put operation but it is part
// of the multipart transaction.
//
// Implements S3 compatible Upload Part API.