उपलब्धता (सिस्टम चलु र पहुँचयोग्य छ) र विश्वसनीयता (सिस्टम सही तरीकाले काम गर्छ) मुख्य गैर-कार्यात्मक आवश्यकताहरू हुन्। तिनलाई प्राप्त गर्न redundancy, fault tolerance, एकल विफलता बिन्दु हटाउने, र विफलताहरू सहृदय तरीकाले हेर्न समावेश छ।
उपलब्धता बनाम विश्वसनीयता
AVAILABILITY → the system is UP and responsive (accessible when needed):
→ measured as uptime % ("nines": 99.9% = ~8.7h/year down; 99.99% = ~52min/year)
RELIABILITY → the system works CORRECTLY (does what it should, without failures/errors):
→ related but distinct (a system can be up but returning wrong results — available but
unreliable)
→ both matter: users need the system available AND working correctly.
