  Context: The galaxy cluster Abell S1101 (S1101 hereafter) deviates
significantly from the X-ray luminosity versus velocity dispersion relation
(L-sigma) of galaxy clusters in our previous study. Given reliable X-ray
luminosity measurement combining XMM-Newton and ROSAT, this could most likely
be caused by the bias in the velocity dispersion due to interlopers and low
member statistic in the previous sample of member galaxies, which was solely
based on 20 galaxy redshifts drawn from the literature. Aims: We intend to
increase the galaxy member statistic to perform a precision measurement of the
velocity dispersion and dynamical mass of S1101. We aim for a detailed
substructure and dynamical state characterization of this cluster, and a
comparison of mass estimates derived from (i) the velocity dispersion (M_vir),
(ii) the caustic mass computation (M_caustic), and (iii) mass proxies from
X-ray observations and the Sunyaev-Zeldovich (SZ) effect. Methods: We carried
out new optical spectroscopic observations of the galaxies in this cluster
field with VIMOS, obtaining a sample of ~60 member galaxies for S1101. We
revised the cluster redshift and velocity dispersion measurements based on this
sample and also applied the Dressler-Shectman substructure test. Results: The
completeness of cluster members within r200 was significantly improved for this
cluster. Tests for dynamical substructure did not show evidence for major
disturbances or merging activities in S1101. We find good agreement between the
dynamical cluster mass measurements and X-ray mass estimates which confirms the
relaxed state of the cluster displayed in the 2D substructure test. The SZ mass
proxy is slightly higher than the other estimates. The updated measurement of
the velocity dispersion erased the deviation of S1101 in the L-sigma relation.
