# Centralized vs. Decentralized Cloud Computing in Healthcare
## 6 Decentralized Cloud Computing
The model uses a hybrid cloud architecture, where patient data of a sensitive nature are stored in a private cloud to provide heightened protection and management, whilst public data are maintained in a public cloud for general healthcare information. NoSQL databases offer cost savings and scalability. They can handle larger data volumes at a lower cost and with less infrastructure. However, combining RDBMS and NoSQL databases to implement a distributed storage system is complex and requires expertise in both technologies. This may increase system complexity, making maintenance and troubleshooting more challenging. The document discusses the challenges of managing large volumes of structured and unstructured data using traditional DBMS. However, it does not quantify the performance improvements achieved by the proposed hybrid RDBMS-NoSQL approach. Meanwhile, ref. [72] highlighted the significance of secure data storage in healthcare databases hosted on decentralized cloud storage systems. The implementation of a backup proxy server for ad hoc data recovery contributes to faster data access and retrieval, as the system can quickly recover data from the proxy server if needed. The system employs robust encryption methods, such as AES-256 and Paillier encryption, to secure patient data for storage on distributed servers. Role-based access control (RBAC) and attribute-based encryption (ABE) guarantee that only authorized individuals may retrieve the encrypted patient data, preserving privacy. Data are dispersed among numerous servers, and hashing methods are used to enhance security and prevent unwanted access or tampering with the data. The backup proxy server approach offers a cost-effective solution for data recovery and redundancy. It can utilize more economical storage options compared to the primary data servers. However, introducing the backup proxy server may result in an additional step in the data access process, potentially increasing latency based on the server's location and performance. However, the creation of an RBAC system for secure data access is time-consuming, and large AES 256 encryption key sizes can slow data access, which delays efficient communication for the end users. In [73], a community cloud architecture was designed to improve the accessibility of healthcare data. The platform allows clinicians, researchers, and data scientists to access datasets from multiple sources easily. The architecture employs a cloud-based design configuration to ensure fast processing and scalable data analytics. Cloudlets are small-scale cloud infrastructures deployed near end-users, providing low-latency access to data and applications. The architecture was intentionally designed to not store or cache any sensitive data to prevent potential attacks. Instead, the data are removed from the cloud after the termination of each remote desktop session. The architecture ensures compliance with security standards such as HIPAA and NIST [74], which are crucial for protecting sensitive patient health data's confidentiality and integrity. The secure gateway component provides a mechanism for secure data transformation and access control, ensuring that patient data are properly anonymized and access is exclusively allowed to individuals who have been approved. The use of Virtual 641 Desktop Infrastructure (VDI) and thin-client access further enhances data privacy by keeping sensitive data centralized and limiting the exposure of raw data on end-user devices. The design based on cloudlets and the VDI approach enables efficient resource utilization 644 and scalability, leading to reduced overall infrastructure and maintenance costs. However, the system utilizes a query parallelization mechanism that allows users to run multiple queries simultaneously. However, this has led to an increase in hardware costs and power 647 consumption. Table 3 summarizes the studies discussed above, in terms of their advantages and limitations.