  Maximum distance separable (MDS) codes facilitate the achievement of elevated
levels of fault tolerance in storage systems while incurring minimal redundancy
overhead. Reed-Solomon (RS) codes are typical MDS codes with the
sub-packetization level being one, however, they require large repair bandwidth
defined as the total amount of symbols downloaded from other surviving nodes
during single-node failure/repair. In this paper, we present the {\em set
transformation}, which can transform any MDS code into set transformed code
such that (i) the sub-packetization level is flexible and ranges from 2 to
$(n-k)^{\lfloor\frac{n}{n-k}\rfloor}$ in which $n$ is the number of nodes and
$k$ is the number of data nodes, (ii) the new code is MDS code, (iii) the new
code has lower repair bandwidth for any single-node failure. We show that our
set transformed codes have both lower repair bandwidth and lower field size
than the existing related MDS array codes, such as elastic transformed codes
\cite{10228984}. Specifically, our set transformed codes have $2\%-6.6\%$
repair bandwidth reduction compared with elastic transformed codes
\cite{10228984} for the evaluated typical parameters.
