On the 27th, the server room, the core space of Naver's second data center, "Gak Sejong." After passing through the security door, the sound of Nvidia H100 GPUs (graphics processing units) in operation blended with the cooling equipment noise and rang in the ears. Thinking it might be hot from the heat emitted in the server room, I started to take off my outerwear but soon pulled my collar tight. Contrary to expectations, cold air blew from both ends of the room, enough to feel a gentle breeze. Here, natural air cools the server room 24 hours a day. In spring and fall, outside air is used directly. In summer and winter, warm air from inside the server room is mixed with outside air to control temperature and humidity. This is because it uses the hybrid system "Namu III (NAMU·NAVER Air Membrane Unit)." Thanks to this, the server room is maintained at an appropriate temperature of 22–26 degrees.
Upon entering "Gak Sejong" on Haengbok-daero in Sejong Special Self-Governing City that day, a massive gray building came into view. On a 294,000㎡ (square meters) site the size of 41 soccer fields, the North Wing in operation was so large that the entire building could not be taken in at a glance. The North Wing measures 350 meters in length—longer than laying the 63 Building on its side—and consists of five floors: three underground and two above ground. The name "Gak" is derived from "Janggyeonggak," which housed the Tripitaka Koreana in the Goryeo era. Naver opened its second data center, "Gak Sejong," in 2023, 10 years after operating its first data center, "Gak Chuncheon." While Gak Chuncheon serves Naver services such as search, Gak Sejong is the company's future core base for providing generative artificial intelligence (AI) services and external cloud services.
In the IT warehouse here, the robots "Sero," which removes, inserts, and manages servers, and "Garo," which moves heavy assets between the server room and the warehouse, were busily moving around. In particular, Sero is designed to match the 3.2-meter height of the server racks, transporting server racks to high spaces that are hard for workers to access. The Garo robot can lift up to 400 kg. Thanks to Sero and Garo, workers' task time is expected to be reduced by up to 50%.
Naver is currently using about one-sixth of the "Gak Sejong" space. The data center has a phased plan for expansion through the sixth phase. The company plans to go through a three-stage expansion in the North Wing and then proceed with phases four to six in the South Wing. Upon full expansion, it can accommodate 600,000 units (unit, a standard height measure for servers) of servers, the largest level in Korea. This is a scale that can store 65 exabytes of data, about 1 million times the total data of the National Library of Korea. It is designed to supply up to 270 megawatts of power.
Gak Sejong is busy preparing for phase-two and phase-three expansions just two years after opening. Noh Sang-min, head of the Naver Cloud data center, said, "As the pace of AI data growth accelerates, we are proceeding with phase-two and phase-three expansions simultaneously," and added, "We plan to break ground by January at the latest, complete the phase-two expansion in 2028, and complete the phase-three expansion in 2029."
Heat management is also a focus in the expansions. Heat management is one of the core competitive strengths of data centers where AI computation is concentrated. As GPU power density increases, cooling technology dictates efficiency and stability. Noh said, "For the phase-two and phase-three expansions, we plan to introduce the 'direct liquid cooling (DLC·Direct Liquid Cooling)' system as the basic design," adding, "Through this, we plan to raise the maximum power per rack from 30 kW to over 50 kW." The liquid cooling system compensates for the shortcomings of existing air-cooling systems, which have poor energy efficiency and severe fan noise. It also appears to take into account that next-generation servers such as Nvidia's B200 and B300 require DLC-based solutions. They are also testing the feasibility of the tank-type immersion liquid cooling (ILC·Immersion Liquid Cooling) method, in which servers are directly immersed in liquid. The message is that the heat management approach will be adjusted depending on market conditions at the time of expansion.
Lee Sang-jun, Naver Cloud chief information officer (CIO), said, "AI infrastructure competitiveness depends not only on the number of GPUs corporations have secured but also on how stably and efficiently those resources are operated," adding, "Unlike big tech that makes massive investments in AI businesses, we must pursue an efficient approach."
Naver also emphasized the safety of Gak Sejong that day. Batteries and lack of separation between the battery and the server room have been cited as causes of the recent fire at the National Information Resources Service computer room, and the paralysis of the administrative information system has been a hot topic. Noh Sang-min, head of the data center, said, "Gak Sejong is designed with a redundant structure that completely separates yet organically integrates power, cooling, and server operation systems so that services do not stop even in the event of a failure," adding, "Naver also has data centers that can provide backup, so we can reroute and normalize services and are relatively well prepared." Gak Sejong also structurally blocks fault propagation by rearranging UPS (uninterruptible power supply) and power distribution facilities to match the high-power characteristics of GPU servers.
Asked how long recovery would take if a situation like the National Information Resources Service fire occurred at Gak Sejong, CIO Lee Sang-jun said, "There would be an impact, but since we have continuously invested in dualization, I think we could recover somewhat faster." In addition, Gak Sejong is designed to withstand an earthquake of magnitude 7.0. This is a special-class seismic design applied to buildings at the level of nuclear power plants.