  In this paper, we investigate the effect of incorrect disk replacement
service on the availability of data storage systems. To this end, we first
conduct Monte Carlo simulations to evaluate the availability of disk subsystem
by considering disk failures and incorrect disk replacement service. We also
propose a Markov model that corroborates the Monte Carlo simulation results. We
further extend the proposed model to consider the effect of automatic disk
fail-over policy. The results obtained by the proposed model show that
overlooking the impact of incorrect disk replacement can result up to three
orders of magnitude unavailability underestimation. Moreover, this study
suggests that by considering the effect of human errors, the conventional
believes about the dependability of different RAID mechanisms should be
revised. The results show that in the presence of human errors, RAID1 can
result in lower availability compared to RAID5.
