AWS Snapshots are “Crash-consistent” by default. This means that when you back up an EC2 instance at a certain time, and later want to restore this instance from backup, it will start the same as a machine that had its power cord pulled out (i.e. booting after a power outage). The file system and any other applications (i.e. a database) using EBS volumes were not prepared or even aware that a backup was taking place, so they may have been in the middle of an operation or transaction and these will be lost. In order remediate to this problem you need Application-Consistent backups (which freeze operations and include transactions in the backup session from the RAM).