Using both keep-last and keep-hourly together on Proxmox Backup Server (PBS) is redundant and causes confusion because both rules target the newest snapshots, leading to an overlapping “safety floor” that retains more backups than intended.
keep-last N ignores calendar time completely and blindly keeps the N newest snapshots regardless of when they were taken. If you run backups hourly, keep-last 24 keeps the last 24 individual snapshots.
keep-hourly N keeps the newest snapshot for each of the last N hours. If you run hourly backups, this already covers the exact same recent hourly window.
Evaluation order: PBS evaluates rules sequentially (keep-last, then hourly, daily, weekly, monthly, yearly) using OR logic. Combining a high keep-last with keep-hourly means you are stacking two overlapping rules for recent backups, preventing older buckets from pruning cleanly.
Fix:
Proposed standard (Grandfather-Father Son retention profile):
keep-hourly: 24 (last 24 hours)
keep-daily: 7 (last 7 days)
keep-weekly: 4 (last 4 weeks)
keep-monthly: 12 (last 12 months)
keep-yearly: 1 (or more i.e. 99)