Centera - SuicidePreventionManager AvailableCapacityPercent

We have an old Centera that I don't know a lot about.  I thought I've been maintaining space on it but I recently received an error stating:

$Server.Product.SuicidePreventionManager.Main.AvailableCapacityPercent@$CLUSTER:c001n02:78212dc6-1dd2-11b2-ad8d-d07fe5076898:threshold2 (9%)

We use the Centera for an email archive.  I've removed some of the older archives and have run the garbage collection.  The garbage collection recovers space.  Below is what the cluster capacity looks like.  When I run the garbage collection the available capacity goes up.  Am I not purging enough of the older email archives to get this error under control?  Or is there something else I should be looking at and doing to recover the Main.AvailableCapacityPercent?  Any help would be appreciated.

Cluster Capacity