Amazon's S3 data-storage service was down for several hours on Friday morning, leaving businesses that rely on the service offline.

S3 is used by companies to store and quickly retrieve large amounts of data, often to run websites and services.

An Amazon spokesman said that one of three geographic locations for the service was unreachable for about two hours, but that it was operating at 99 percent of normal performance by Friday afternoon, UK time. "We've been communicating with our customers all morning via our support forums and will be providing additional information as soon as we have it," said Drew Herdener.

Many customers appeared not to have gotten that communication. They complained on the forum about a lack of information from Amazon about the outage and when it would be fixed. One suggested that Amazon could have at least posted a message on the front page of the web-services site, so that customers would be aware that the problem wasn't on their end.

Others wrote about the problems that the outage was causing their businesses. "It's becoming very embarrassing for us here," one wrote. "We desperately need an update... it's a huge hit on our reputation."

Many of the users said that the service was down for around three hours.

Gustavo, a user in Brazil, said that his company hosts more than 30,000 images from a large television station in Brazil. "Now we are having several problems because of this S3 issue," he wrote. "My company chose to work with Amazon because of its reliability."

Late last year, Amazon introduced a new service level agreement for S3 that guaranteed 99.9 percent uptime each month. If the service slips below that level, the company promised to provide service credits to certain users.