The document discusses Pinterest migrating their Apache Spark clusters from HDFS to S3 storage. Some key points: 1) Migrating to S3 provided significantly better performance due to the higher IOPS of modern EC2 instances compared to their older HDFS nodes. Jobs saw 25-35% improvements on average. 2) S3 is eventually consistent while HDFS is strongly consistent, so they implemented the S3Committer to handle output consistency issues during job failures. 3) Metadata operations like file moves were very slow in S3, so they optimized jobs to reduce unnecessary moves using techniques like multipart uploads to S3.