Amazon Web Services, the dominant provider of cloud computing services, has seen a gradual dip in its annual sales growth rate over the past two quarters. Part of that is a natural slowdown as AWS gets bigger—its sales now top $25 billion a year—and faces growing competition. But it could also reflect a shift in the cloud computing business as customers find ways to save money on one of the earliest cloud services: data storage.

While AWS posted a still-strong 37% increase in sales last quarter, that was down markedly from the 49% rate in the second quarter of 2018. Last year's robust growth represented an acceleration in revenue increases after two years of slowing growth. This year, the growth rate has resumed its downward slide, as the accompanying chart shows. The latest quarter was the first time AWS’ growth rate has dipped below 40% in any quarter since Amazon began disclosing the cloud unit's revenue in 2015.