  An $(n,k)$ maximum distance separable (MDS) code has optimal repair access if
the minimum number of symbols accessed from $d$ surviving nodes is achieved,
where $k+1\le d\le n-1$. Existing results show that the sub-packetization
$\alpha$ of an $(n,k,d)$ high code rate (i.e., $k/n>0.5$) MDS code with optimal
repair access is at least $(d-k+1)^{\lceil\frac{n}{d-k+1}\rceil}$. In this
paper, we propose a class of multi-layer transformed MDS codes such that the
sub-packetization is $(d-k+1)^{\lceil\frac{n}{(d-k+1)\eta}\rceil}$, where
$\eta=\lfloor\frac{n-k-1}{d-k}\rfloor$, and the repair access is optimal for
any single node. We show that the sub-packetization of the proposed multi-layer
transformed MDS codes is strictly less than the existing known lower bound when
$\eta=\lfloor\frac{n-k-1}{d-k}\rfloor>1$, achieving by restricting the choice
of $d$ specific helper nodes in repairing a failed node. We further propose
multi-layer transformed EVENODD codes that have optimal repair access for any
single node and lower sub-packetization than the existing binary MDS array
codes with optimal repair access for any single node. With our multi-layer
transformation, we can design new MDS codes that have the properties of low
computational complexity, optimal repair access for any single node, and
relatively small sub-packetization, all of which are critical for maintaining
the reliability of distributed storage systems.
