Shares of QTS Realty Trust (formerly known as Quality Technology Services) were down slightly after-hours on the first day of trading on the New York Stock Exchange.

The company's CEO Chad Williams rang NYSE's opening bell Tuesday morning, as its shares started trading at US$21 under the ticker symbol “QTS.” The price reached $22.81 at one point during the day before coming down to $20.96 after hours.

QTS, one of the biggest data center service providers in the US, was the second company in this space to go through an initial public offering this year. The first one was CyrusOne, whose shares started trading on Nasdaq in January.

CyrusOne had a better first day of trading than did QTS. The former's shares opened at $19 per share and went up 12% during the day of the debut.

QTS planned to raise up to $257.25m through the IPO. CyrusOne raised $313.5m in January.

Both companies converted to real estate investment trusts (REIT) simultaneously with going public. Operating as a REIT – other well-known data center REITs include Digital Realty Trust, CoreSite and DuPont Fabros – allows real estate companies to pay substantially lower taxes.

Another data center provider filed for an IPO last month. IO, known for its modular data center product IO.Anywhere, filed its papers with US regulators anonymously, which means nearly no details were available about the company's plans for the offering.

“Today marked an important day in the history of QTS as we began trading on the New York Stock Exchange,” Williams said. “I am humbled to be in a position to take our small, family-owned company, started by my father, James Williams, in 1962, to the next level.”

QTS owns, operates and manages about 3.8m sq ft of data center property around the country and serves about 850 customers.

Click here to watch the video of Williams, surrounded by family and colleagues, ringing the opening bell at NYSE on Tuesday morning.