Why you should upgrade Proxmox from 8.x to 9.x
Proxmox 9.x brings significant improvements to the virtualization platform. The one that caught my attention was the built-in ZFS ARC size configuration — it allowed me to reduce ZFS memory usage from 24GB down to 8GB on a 32GB server.
The upgrade process
The upgrade itself is straightforward. The official guide covers every step: Upgrade from 8 to 9.
Before upgrading, I ran the pve8to9 checker which flagged a couple of things I had to fix first: a role change for PVEMonitor and a missing Intel microcode package.
After fixing those, the rest of the process went smoothly — update repos, apt dist-upgrade, reboot, done.
The result: ZFS ARC memory reduction
This is why I upgraded. On Proxmox 8.x, ZFS ARC was consuming around 24GB of my 32GB of RAM with no easy way to cap it from the UI. After upgrading to 9.x, I was able to configure the ARC size limit directly and bring it down to 8GB — freeing up 16GB for VMs and containers.
The system is running smoothly and I finally have headroom to spin up more workloads without worrying about ZFS eating all available memory.
Conclusion
If you're running Proxmox with ZFS and struggling with high memory usage, the upgrade to 9.x is worth it just for the ARC configuration alone. The upgrade process is low-risk if you follow the official guide, and the payoff is immediate.
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