Want a petabyte for under US$120,000?

The online backup service provider formed in January 2007 and launched in the middle of last year using with a Dell system. Backblaze then experimented with an array of external mini-NAS boxes connected to a central computer to handle its expanding storage requirements.

"It's been quite a rocket ride. We launched the Windows version in September 08 and we launched the Mac version in April this year," said Budman. "We added a petabyte for our customers in the last six months. Facebook's entire photo storage is a PB and a half, and we've had that for the past year."

The company gives individuals and businesses unlimited backup for US$5 per machine per month. A competitor, EMC-owned Mozy, also gives users unlimited backup for the same price.

However, this offer is restricted to home users and is also throttled to prevent uploading large amounts of data, said Budman.

The company's business model requires cheap storage to make a profit on its unlimited backup offer. Budman realised he needed to build the storage units to make the business viable.

"We couldn't make a profit on it if we had bought the equipment. We wanted to offer a fixed price because nobody really knows how much data they need to backup. We didn't want people to worry about whether they had enough space," said Budman.

"We are one of the few companies for whom this was a necessity to do. There aren't a lot of companies that have the scale requirements in needing petabytes of storage and also have the cost pressures, where it's critical to have it cost effective."

The company committed to building its own pod and drew on support from outside the company to design the system.

Budman said the process was not as easy as they first thought. "We thought that hardware was like building blocks, like lego, and you put it together and it just works. But it took a while to get right."

Backblaze has been using the pods for a year which provide a petabyte and a half of storage. Reliability issues have been ironed out; Budman said the company replaces one drive a week in the whole set-up.

None of the pods themselves have failed, he said. "It's only been a year but the pods themselves are brand name components for the most part and they've been solid."

Backblaze discovered that the type of drive made a difference to the pod's operation. It has standardised the pods on 1.5TB Seagate drives because they offered the best combination of price, performance and reliability.

"We expected that one drive would be the same as another, but we found that some drives performed better and some worse," said Budman.

Read on for why Backblaze chose Debian as the operating system.