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 state

This 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.

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✅ 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.

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