One wrong parameter can delete 30 days of data. 3. **"The right block size is free performance."** — No code changes, just JCL and data classes. 4. **"SHAREOPTIONS 3 is the Wild West."** — Use SHAREOPTIONS 2 or VSAM RLS for integrity. 5. **"Pre-recall, don't auto-recall."** — Proactive HSM recall be