Step-by-Step Guide

Keeping an eye on your storage usage is essential — especially before you run out of space unexpectedly. In this guide, you’ll learn how to set up a PRTG REST Custom v2 sensor to monitor your Hetzner Storage Box in real time, including used space, snapshot usage, and a percentage-based alert when capacity runs low.

PRTG Sensore view

 

Prerequisites

Before you begin, make sure you have:

  • A running PRTG Network Monitor instance
  • A Hetzner API token with read access
  • Your Storage Box ID (visible in the Hetzner Cloud Console)

Step 1: Add a New REST Custom v2 Sensor

In PRTG, navigate to the device where you want to add the sensor, click Add Sensor, and search for REST Custom v2.

Fill out the sensor form with the following values:

Field Value
Request URL https://api.hetzner.com/v1/storage_boxes/[YOUR_STORAGE_BOX_ID]
Custom HTTP Headers Authorization: Bearer YOUR_API_TOKEN

Replace [YOUR_STORAGE_BOX_ID] with your actual Storage Box ID and YOUR_API_TOKEN with your Hetzner API token.

Step 2: Configure the Channels

Add the following five channels to capture all relevant storage metrics:

Channel 1 — Total Available Size

JSONPath: $.storage_box.storage_box_type.size
Name: Available Size  |  Value Type: Integer  |  Unit: Bytes (Disk)

Channel 2 — Total Used Space

JSONPath: $.storage_box.stats.size
Name: Used (Total)  |  Value Type: Integer  |  Unit: Bytes (Disk)

Channel 3 — Used Data Space

JSONPath: $.storage_box.stats.size_data
Name: Used Data  |  Value Type: Integer  |  Unit: Bytes (Disk)

Channel 4 — Used Data (Percentage)

JSONPath: $.storage_box.stats.size_data
Name: Used Data %  |  Value Type: Integer  |  Unit: Bytes (Disk)

This channel will be configured to show a percentage value in the next step.

Channel 5 — Snapshot Usage

JSONPath: $.storage_box.stats.size_snapshots
Name: Used Snapshots  |  Value Type: Integer  |  Unit: Bytes (Disk)

Sensor Settings

Step 3: Configure the Percentage Channel

Once the sensor is saved and collecting data, you need to fine-tune the Used Data % channel to display a meaningful percentage value.

  1. Open the sensor overview and click Edit on the Used Data % channel.
  2. Under Data, switch the display mode to “Display in percent of maximum”.
  3. Enter the maximum size of your Storage Box as the reference value (e.g., 1099511627776 for a 1 TB box).

This will give you an accurate percentage of how full your storage is, rather than a raw byte value.

Edit Channel

Edit Channel

Step 4: Set Up an Alert Trigger

Now that the sensor is running, add a notification trigger so you get alerted before your storage fills up completely.

  1. Go to the sensor and click “Notification Triggers”.
  2. Add a new Threshold Trigger with the following settings:
Setting Value
Channel Used Data % (Byte)
Condition Is above 95
Duration For at least 60 seconds
Action Send Email & Push Notification to Admin
When cleared Send Email & Push Notification to Admin

Notification Triggers

This example alerts when more than 95% of capacity is used (less than 5% free). Adjust the threshold to match your own requirements — for example, use 90 if you want to be warned when less than 10% remains.

Summary

With this setup, PRTG will continuously poll the Hetzner API and give you full visibility into your Storage Box usage — broken down by data and snapshots — with a clear percentage view and proactive alerting before you run into capacity issues.

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