In the maintenance phase of the SDLC, the goal is to ensure the system continues to meet business needs by fixing defects, applying updates, and implementing enhancements. This phase ensures the system remains secure, reliable, and effective after deployment.

Option B: Gathering requirements occurs in the planning/analysis phase.

Option C: Unit testing is part of the testing phase, not maintenance.

Option D: Designing and deploying the architecture occurs in development and implementation phases.

Thus, the goal of the maintenance phase is to fix defects and update the software.