Facebook will extend one of the buildings in its Altoona data center cluster, after three previous expansions at the Iowa location.

The latest addition will be a 100,000 sq ft (9,290 sq m) cold storage facility to store photos users access rarely.

Selfies from when you were young

This fourth expansion is the latest from Facebook’s “construction teams who have worked onsite since 2013,” Brice Towns, Altoona data center site manager said in a Facebook post.

“These teams have put in 830,000 hours into building one, 760,000 hours into building two, nearly 840,000 hours into building three, and now in less than four months, we’ve already seen more than 7,500 hours on our cold storage facility.”

The first phase of the Altoona data center was a 476,000 sq ft (44,221 sq m), $300 million construction, the second was a 468,000 sq ft (43,478 sq m) building, and the third a 496,000 sq ft (46,079 sq m) facility.

The new cold storage facility comes after Facebook’s Prineville and Forest City data centers also had cold storage sites added.

In May 2015, Facebook software and infrastructure engineers Krish Bandaru and Kestutis Patiejunas described the company’s cold storage tech.

They said: “The data centers are equipped with less than one-sixth of the power available to our traditional data centers, and, when fully loaded, can support up to one exabyte (1,000 PB) per data hall. 

“Since these facilities would not be serving live production data, we also removed all redundant electrical systems — including all uninterruptible power supplies (DCUPS) and power generators, increasing the efficiency even further.”