Security is considered to be one of the most critical aspects in a cloud computing environment due to the sensitivity and importance of information stored in the cloud and also because the management of the data might not be fully trustworthy. The risk of malicious insiders in the cloud and the failing of cloud services have received a strong attention by companies. Security brings in concerns for data confidentiality, in addition to integrity and availability. Security has the characteristics of a complement to reliability. This work proposes a new model called Multi-clouds Databases (MCDB) which uses multi-clouds instead of single cloud service provider, such as in Amazon cloud service. The proposed model also incorporates the Shamir's secret sharing approach. In addition, it adopts a triple modular redundancy (TMR) technique with sequential method to improve the proposed cloud computing systemreliability and then enhance the security aspect.