Purpose of vent holes on the top of rackmount servers?

Solution 1:

(Some people are hard to please...)

These are likely system exhaust vents and fit into the total design of the product. Please understand that the system is designed and optimized for rack mounting in a proper enclosure with separation between hot and cold air aisle. These servers are designed to be placed in adjacent rack units, and there's a small gap that fits within the envelope of the rack unit standard.

To allow space between adjacent rack-mounted components, a panel is 1⁄32 inch (0.031 inch or 0.79 mm) less in height than the full number of rack units would imply.

That's the primary use case for this type of server and drives the product development target. When I say "total design", that may include factors like thermal management, vibration, fan speed, power consumption and acoustics.

If you see vents and don't understand why they may be there, possibilities could include eliminating known hot-spots or being part of an internal air circulation strategy for different potential configurations. There's already internal baffling and shrouding to help direct airflow between zones. These may simply be exhaust vents for air, heat or both. Maybe the server vibrates less with their presence, or perhaps the vents change the timbre of the fan sound.

Sometimes, you may see a design element meant for an edge case, like a fully-loaded PCIe riser cage or for a minimal configuration like a single CPU and single power supply. Or maybe it's relief for a situation where the server is sitting and running on a workbench or table. Perhaps this type of venting allows the server to run with a lower fan speed and rely more on passive heat dissipation. That can address both acoustic and power efficiency goals.

For instance, the rear-right edge of my HP ProLiant DL360p Gen8 1U rack mount server is the location of the 10GbE NIC module and the embedded RAID controller. There's also room for a PCIe card in the same spot.

• The present temperature at that specific location inside the server is 183°F (84°C).
• The threshold for that location is 221°F (105°C).
• There are perforations in the server's top cover at that location.
• With a full PCIe load, these perforations serve as exhaust and it makes sense that there would be accommodations at that hotspot.

My suggestion is to use the server as designed and indicated by the manufacturer. If you don't have a full rack and proper datacenter environment or will be operating in less-than-ideal conditions, make sure that the server's vents are unobstructed. Monitor your system's vitals, since this equipment is designed to record, report and react to its surroundings. Otherwise, I wouldn't worry too much about this.

Solution 2:

Those holes are IMHO there to allow the air to keep venting in the event a person fills the expansion slots. Cards in expansion slots don't have vent holes so each care is removing venting real estate.

Plus, if you are racking properly, the servers shouldn't actually touch each other. Granted the gap is small but it's enough to allow air to pass through those rear-ward, top vent holes.

Solution 3:

Servers aren't really intended to be stacked directly on top of each other but for mounting in a 19'' cabinet. Typically there they don't quite touch and those vent holes won't be (completely) closed off.

For their actual purpose, I can only guess... Either to allow airflow and prevent excessive pressure differences when the main intake and outflow aren't quite balanced?

Or maybe to allow thermal circulation for when the server is switched off. Then you'd still want to have the possibility for circulation and a way for any remaining heat to escape.