Here’s a concise but detailed summary of the issue we encountered and how we resolved it:
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🛑 Issue Summary: VM Refused to Start (VMID 101) on Proxmox
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we attempted to start our Windows Server 2025 VM (VMID 101) but received conflicting signals:
• qm start 101 claimed the VM was already running
• However, qm status 101 reported status: stopped
• The Proxmox web interface showed Start button greyed out, giving the impression of a hung or inconsistent stateThis was concerning, especially because we were remotely connected, and any VM startup failure could disrupt access or services.
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🧠 Diagnosis
• Proxmox was unable to allocate memory for the VM.
• The VM was configured to use 54 GB of RAM.
• The system has 64 GB of physical RAM, but no swap space was configured yet.
• ZFS (used as our storage backend) also consumes a significant amount of RAM, leaving insufficient headroom for the VM to launch.⸻
✅ Solution: Create and Enable Swap Space
We mitigated the issue by creating a 64 GB ZFS-based swap volume, ensuring the system could allocate memory more flexibly:
1. Create ZFS Swap Volume:zfs create -V 64G rpool/swap
2. Format it for swap:mkswap /dev/zvol/rpool/swap
3. Activate it immediately:swapon /dev/zvol/rpool/swap
4. Make it permanent by adding to /etc/fstab:echo ‘/dev/zvol/rpool/swap none swap defaults 0 0’ >> /etc/fstab
5. Optional: Tune swappiness (to reduce reliance on swap except under pressure):echo ‘vm.swappiness=10’ >> /etc/sysctl.conf
sysctl -p
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📈 Result
• Swap space is now active:swapon –show
shows 64 GB available.
• The VM now starts reliably.
• We have a safety cushion for memory exhaustion scenarios, even with high-ZFS memory demand.⸻