FreePBX includes a backup script that can consume 100% of CPU and DISK resources. HAAst will accurately detect that Asterisk has become unresponsive (during this backup window) and will correctly initiate a failover. We recommend that you disable the automatic launch of the backup script from within FreePBX. Then you can either launch the FreePBX backup script from cron using ionice and nice to make it behave properly (better), or switch to a professional backup program (eg: Backup Exec Linux Agent).
