Proxmox VE 8 (Debian 12) support ends August 2026. PVE 9 (Debian 13) in-place upgrade guide: pve8to9 pre-check, APT sources Bookworm→Trixie, dist-upgrade, cluster rolling upgrade, VM compatibility (machine version, virtio drivers), ZFS rollback scenario, and common issues.
Practical implementation of the 3-2-1-1-0 backup rule with Proxmox Backup Server (PBS): ZFS datastore, deduplication, retention/prune/GC schedules, offsite sync to a second PBS, PBS 4.2 S3 backend, and external S3 Object Lock for immutable backups. Complete ransomware protection. Includes version compatibility table.