A forgotten server still draws power
Machine room, part 4: almost every server room has a device that nobody needs any more and nobody wants to switch off. It draws power, has to be cooled and occupies rack units. What the Energy Efficiency Act requires, why switching off fails on ownership, and how to find ghost servers without hitting a production server.
A server room in the basement of an administrative building. In the fourth rack, rack units 12 and 13, a server with green lights. The label shows a project name from 2019. It does not appear in the list of IT systems. The colleague who set it up moved to another department two years ago. Nobody knows what it does. And that is why nobody switches it off.
A device like this costs three times: the power it draws itself, the cooling that has to remove that power from the room again as heat, and the rack units that are missing for a new device. On top of that comes a risk that appears in no energy balance: a server nobody knows about does not get updates either.
What the law requires
For data centres within the meaning of the German Energy Efficiency Act (which ones those are was the topic of part 2), Section 12(1) EnEfG requires an energy or environmental management system. Subsection 2 says what has to happen within it: continuous measurements of the electrical power and energy demand of the essential components of the data centre, and measures that continuously improve the energy efficiency of the data centre. In German:
„1. kontinuierliche Messungen zur elektrischen Leistung und zum Energiebedarf der wesentlichen Komponenten des Rechenzentrums durchzuführen und 2. Maßnahmen zu ergreifen, die die Energieeffizienz des Rechenzentrums kontinuierlich verbessern.“
Under subsection 5, this applies accordingly to operators of information technology, including anyone whose servers are housed in someone else's data centre. The law does not say which measures these must be. Switching off a device that no longer has a task is the cheapest measure there is: no investment, no rebuild, and the saving starts the same day. This part is based on the 2023 version; the amendment to the EnEfG has not yet been promulgated.
Where it breaks in practice
On ownership. Switching off needs someone who says yes. If a device is not assigned to any IT system or business application, that someone does not exist. The question travels through three mailboxes and gets stuck in the fourth.
On the wrong test. A server not answering a ping does not mean nobody uses it. A server answering does not mean anyone needs it. A more reliable question is whether the device still talks on the network at all: whether its MAC address has appeared in a switch table in recent weeks. And where that observation is missing, the answer is not "unused" but "unknown".
On the occupancy plan. A rack with twenty free rack units looks like reserve on the plan. If its power limit has been reached, it still takes no more devices. Ghost servers are often why space and power do not match: they use up the budget the next device is missing.
A proven approach is to first only disconnect the network instead of switching the device off, and to announce a deadline. If nobody comes forward in that time, it is switched off, removed after a further deadline, and the drives are wiped or destroyed according to the organisation's rules.
How isidaten handles this
In DCIM, the "ghost candidates" report lists devices that are switched on and active, have a measured power draw or rated value above 0 watts, are not assigned to any IT system and whose device type carries payload; power strips, UPS and patch panels are excluded. A device counts as in use if one of its MAC addresses was learned in a switch table within the last 14 days. Devices without a recorded MAC address, or without switch tables in that period, appear separately as not checkable rather than as ghosts. Every entry carries its reason; the report does not switch anything off. Alongside it, the stranded capacity report shows racks with free space but no power, or free power but no space.
The test question
How many devices in your racks can you assign to an IT system and a responsible person today?
Every device without an answer is not a ghost server. But it is a candidate, and as long as nobody looks, it stays one.
Sources
Energy Efficiency Act (EnEfG), Section 12(1), (2), (5) and (6) (German), version of 13.11.2023, retrieved on 21.10.2026.
In the next part: the emergency power chain is only as good as its last test run. The previous part: A/B is only redundant when each side carries the load alone.
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