Grafana Panel for AWS Lustre FSX (FreeDataStorageCapacity) not working as expected

I am trying to create a panel for monitoring the AWS Lustre FSX in Grafana, a timeseries graph that will show the size reducing over period.


the above is my query condition. This works properly while the time filter is 24 hours or less.

When I change the timefilter to more than 24 hours, the graph is like this.


I can understand that this is an expected behavior since I’m using the “Sum” Statistic.

What I want to achieve is the actual size change over any period of time. Thanks in advance.