As the 2012 holiday season approached, Karmaloop eyed a potential problem—albeit a good one. Traffic was up for the year, and the retailer was worried that come November its site might slow with a heavier holiday load.

To prevent any site performance issues before they arose, Karmaloop in October ramped up its “virtual server” capacity that it rents from its hosting provider Rackspace, says Karmaloop chief technology officer Gary Rush. Virtualization software divides up physical servers into virtual servers that are each able to store data and handle computing tasks the way a physical computer would have in the days before virtualization made it possible to compartmentalize the power of a single machine.

The move helped. Traffic and sales for the holiday period increased about 40% year over year and the site’s response times remained constant.

Much of the traffic increase stemmed from mobile, Rush says. “The mix was different,” he says. “Web traffic was only slightly up but mobile traffic, which was very low in 2011 because we didn’t have much in the way of mobile-specific sites or apps, was up to almost 30% of total traffic and sales.”

Rush says by quickly ramping up its web hosting capacity, Karmaloop.com’s pages loaded in the same amount of time as they do during the non-peak season when fewer consumers visit the site. He adds that the site performed well on Cyber Monday, the Monday after Thanksgiving, even though Karmaloop.com’s sales volume was nearly 600% the site’s normal daily volume. Karmaloop says its Cyber Monday traffic also increased between 250% and 300%.

Karmaloop.com switched to Rackspace around three years ago from a smaller hosting provider and pays what Rush says is a healthy five-figure amount to the vendor each month. The retailer uses Rackspace for its entire production infrastructure, Rush says, including production web servers, database servers, routers, firewalls and switches.

Karmaloop is No. 138 in the Internet Retailer Top 500 Guide.