// the end, this is performed by the caller before
			// closing 'w'.
			if err = disk.DisableDirectIO(file); err != nil {
				return written, err
			}

			// buf is not aligned, hence use writeUnaligned()
			// for the remainder
			un, err = w.Write(buf[len(buf)-remain:])
			nw += int64(un)
		}

		if nw > 0 {
			written += nw
		}

		if err != nil {
			return written, err
		}