Amazon.com offers an online hosted storage service for IT storage buyers known as Simple Storage Service (S3). 

Amazon has just announced that it is offering a new Service Level Agreement (SLA) guarantee for its S3 customers:  those customers will receive an “uptime” service availability of at least 99.9% each month.  In the event the service falls below the 99.9% uptime level of service, Amazon will provide “qualified users” appropriate service credits to be distributed in cases of internal server errors or a "denied request."

A server error is considered to have occurred if an end user pings S3 and receives "InternalError" or "ServiceUnavailable" replies.  The formula for calculating the service credits is complicated and is based on a percentage of charges paid during a particular billing cycle.

The new Service Uptime guarantee program is not accompanied by an upgrade to the hosted service. Amazon claims that its services and SLA will be measured by its track record, rather than by its promises. While this guarantee may be difficult to uphold and to calculate from a billing perspective, online storage services vendors are in such a competitive market that they must offer extraordinary things such as guaranteed SLAs to draw in IT storage buyers as customers.  These customers are seeking and must have highly reliable storage options since their businesses are relying on its reliability, availability and “uptime.”

Read more here.