When I come across interesting innovations or designs notably different from the norm, I love to dig in and learn the details. More often than not I post them here. Earlier this week, Google posted a number of pictures taken from their datacenters (Google Data Center Tech). The pictures are beautiful and of interest to just about anyone, somewhat more interesting to those working in technology, and worthy of detailed study for those working in datacenter design. My general rule with Google has always been that anything they show publically is always at least one generation old and typically more. Nonetheless, the Google team does good work so the older designs are still worth understanding so I always have a look.

Some examples of older but interesting Google data center technology:

· Efficient Data Center Summit

· Rough Notes: Data Center Efficiency Summit

· Rough notes: Data Center Efficiency Summit (posting #3)

· 2011 European Data Center Summit

The set of pictures posted last week (Google Data Center Tech) is a bit unusual in that they are showing current pictures of current facilities running their latest work. What was published was only pictures without explanatory detail but, as the old cliché says, a picture is worth a thousand words. I found the mechanical design to be most notable so I’ll dig into that area a bit but let’s start with showing a conventional datacenter mechanical design as a foil against which to compare the Google approach.

The conventional design has numerous issues the most obvious being that any design that is 40 years old and probably could use some innovation. Notable problems with the conventional design: 1) no hot aisle/cold aisle containment so there is air leakage and mixing of hot and cold air, 2) air is moved long distances between the Computer Room Air Handers (CRAHs) and the servers and air is an expensive fluid to move, and 3) it’s a closed system and hot air is recirculated after cooling rather than released outside with fresh air brought in and cooled if needed.

An example of an excellent design that does a modern job of addressing most of these failings is the Facebook Prineville Oregon facility:

I’m a big fan of the Facebook facility. In this design they eliminate the chilled water system entirely, have no chillers (expensive to buy and power), have full hot aisle isolation, use outside air with evaporative cooling, and treat the entire building as a giant, high-efficiency air duct. More detail on the Facebook design at: Open Compute Mechanical System Design.

Let’s have a look at the Google Concil Bluffs Iowa Facility:

You can see that have chosen a very large, single room approach rather than sub-dividing up into pods. As with any good, modern facility they have hot aisle containment which just about completely eliminates leakage of air around the servers or over the racks. All chilled air passes through the servers and none of the hot air leaks back prior to passing through the heat exchanger. Air containment is a very important efficiency gain and the single largest gain after air-side economization. Air-side economization is the use of outside air rather than taking hot server exhaust and cooling it to the desired inlet temperature (see the diagram above showing the Facebook use of full building ducting with air-side economization).

From the Council Bluffs picture, we see Google has taken a completely different approach. Rather than completely eliminate the chilled water system and use the entire building as an air duct, they have instead kept the piped water cooling system and instead focused on making it as efficient as possible and exploiting some of the advantages of water based systems. This shot from the Google Hamina Finland facility shows the multi-coil heat exchanger at the top of the hot aisle containment system.

From inside the hot aisle, this shot picture from the Mayes County data center, we can see the water is brought up from below the floor in the hot aisle using steel braided flexible chilled water hoses. These pipes bring cool water up to the top-of-hot-aisle heat exchangers that cool the server exhaust air before it is released above the racks of servers.

One of the key advantages of water cooling is that water is a cheaper to move fluid than air for a given thermal capacity. In the Google, design they exploit fact by bringing water all the way to the rack. This isn’t an industry first but it is nicely executed in the Google design. IBM iDataPlex brought water directly to the back of the rack and many high power density HPC systems have done this as well.

I don’t see the value of the short stacks above the heat exchanges. I would think that any gain in air acceleration through the smoke stack effect would be dwarfed by the loses of having the passive air stacks as restrictions over the heat exchangers.

Bringing water directly to the rack is efficient but I still somewhat prefer air-side economization systems. Any system that can reject hot air outside and bring in outside air for cooling (if needed) for delivery to the servers is tough to beat (see Diagram at the top for an example approach). I still prefer the outside air model, however, as server density climbs we will eventually get to power densities sufficiently high that water is needed either very near the server as Google has done or direct water cooling as used by IBM Mainframes in the 80s (thermal conduction module). One very nice contemporary direct water cooling system is the work by Green Revolution Cooling where they completely immerse otherwise unmodified servers in a bath of chilled oil.

Hat’s off to Google for publishing a very informative set of data center pictures. The pictures are well done and the engineering is very nice. Good work!

· Here’s a very cool Google Street view based tour of the Google Lenoir NC Datacenter.

· The detailed pictures released last week: Google Data Center Photo Album


James Hamilton
http://blog.mvdirona.com / http://perspectives.mvdirona.com