Problem

Proxmox shows this warning message:

WARNING: You have not turned on protection against thin pools running out of space.
WARNING: Set activation/thin_pool_autoextend_threshold below 100 to trigger automatic extension of thin pools before they get full.

This warning indicates that LVM thin pools are not configured to automatically extend when they approach capacity, which could lead to VMs running out of disk space unexpectedly.

Solution

Configure LVM to automatically extend thin pools before they become full.

Step 1: Backup Current Configuration

cp /etc/lvm/lvm.conf /etc/lvm/lvm.conf.backup

Step 2: Modify LVM Configuration

Edit /etc/lvm/lvm.conf and update these settings in the activation section:

# Enable auto-extension at 80% capacity
sed -i 's/# thin_pool_autoextend_threshold = 100/thin_pool_autoextend_threshold = 80/' /etc/lvm/lvm.conf

# Extend by 20% when triggered
sed -i 's/# thin_pool_autoextend_percent = 20/thin_pool_autoextend_percent = 20/' /etc/lvm/lvm.conf

Step 3: Verify Configuration

Check that the settings are applied correctly:

grep -A 1 -B 1 "thin_pool_autoextend" /etc/lvm/lvm.conf | grep -E "(threshold|percent)" | grep -v "^#"

Should show:

thin_pool_autoextend_threshold = 80
thin_pool_autoextend_percent = 20

Step 4: Restart LVM Monitoring Service

systemctl restart lvm2-monitor
systemctl status lvm2-monitor

Step 5: Verify Status

Check that logical volumes are being monitored:

lvs

Configuration Explanation

  • thin_pool_autoextend_threshold = 80: Triggers automatic extension when thin pool reaches 80% capacity
  • thin_pool_autoextend_percent = 20: Extends the pool by 20% of its current size when threshold is reached

Example

If you have a 100GB thin pool:

  • At 80GB usage (80%), it automatically extends to 120GB
  • At 96GB usage (80% of 120GB), it extends to 144GB
  • And so on, util you have space on drive…

Benefits

  • Prevents storage exhaustion: VMs won’t suddenly run out of disk space
  • Eliminates warning messages: No more thin pool warnings in Proxmox
  • Automatic management: No manual intervention required for storage expansion
  • Persistent configuration: Settings survive reboots

Monitoring

The dmeventd daemon handles monitoring and automatic extension. Verify it’s running:

ps aux | grep dmeventd

Notes

  • This configuration applies to all thin pools on the system
  • The minimum threshold value is 50% (values below 50 are treated as 50)
  • Automatic extension requires dmeventd to be monitoring the logical volumes
  • Changes take effect immediately and persist across reboots

Alternative: Proxmox Web UI Notifications

For comprehensive storage monitoring, consider configuring email notifications through: Datacenter → Options → Notification in the Proxmox web interface.