## 1 Introduction
### Methodology  
This study systematically examines blockchain-based data storage methods by evaluating their security, scalability, and performance aspects. The study focuses on on-chain, off-chain, and hybrid approaches, analyzing their strengths and weaknesses according to basic criteria. The methodology consists of the following basic stages:  
1. _Selection of Literature and Data Sources_: The literature review used leading scientific databases such as IEEE Xplore, Elsevier ScienceDirect, MDPI, Wiley, Taylor & Francis, and Springer. However, no particular publisher was given priority, and the selection was made based on the content compatibility, contribution to the subject, and up-to-dateness of the studies. 2. _Publication Year Criteria_: Instead of setting a specific year range in the selection of articles, emphasis was placed on recent studies, but basic studies on the subject were also included. In this way, articles considered basic in the literature were also evaluated along with current research trends. In the review process, studies that would provide a comparative evaluation of blockchain data storage solutions in terms of security, scalability, and cost were particularly preferred. In order for the selected references to represent our research scope, it was taken into consideration that they included experimental studies, theoretical frameworks and case studies on different data storage methods. 3. _Search Method_: The literature review process has been carried out with keyword-based searches and key terms such as \"blockchain storage\", \"on-chain vs. off-chain\", \"hybrid blockchain models\", \"Layer-2 scalability\", \"blockchain data security\", \"distributed ledger storage models\", \"blockchain cryptographic techniques\", and \"blockchain storage in healthcare and finance\" have been used. These keywords provided focus on the subject and allowed the inclusion of new trends in the literature. 4. _Comparative Analysis of On-chain and Off-chain Methods_: To establish a solid foundation for the study, a conceptual analysis of on-chain and off-chain storage methods has been conducted in the initial phase. This comparative assessment has facilitated a deeper understanding of the trade-offs involved in different data storage approaches. The study begins with a detailed analysis of on-chain and off-chain data storage methods:  
* The advantages and disadvantages of both methods have been identified and analyzed based on performance, cost, scalability, and data security;
* These insights have contributed to a clearer evaluation of their suitability for different use cases, ultimately supporting the examination of hybrid solutions. 5. _Security Assessment in Blockchain Data Storage Systems_: In this study, various security-related parameters have been systematically examined to assess their implications for blockchain data storage. This evaluation includes the following:  
* Symmetric and asymmetric encryption techniques and their impact on data privacy;
* RBAC and ABAC access control models, comparing their suitability for various applications;
* Hash-based data integrity mechanisms and their effectiveness in preventing security vulnerabilities. _Sectoral Applications of Blockchain Storage Solutions_: In the later stages of the study, the sectoral applicability of blockchain storage solutions has been analyzed. Given the increasing adoption of blockchain technology across different industries, the study particularly evaluates the following: * The use of on-chain, off-chain, and hybrid solutions in key sectors, including healthcare, finance, education, and public administration; * The potential of hybrid approaches in optimizing the balance between security and performance, ensuring practical applicability in real-world scenarios. * _Performance Metrics and Layer-2 Solutions_: To address scalability concerns, Layer-2 solutions have been analyzed as an alternative to enhance blockchain efficiency.