Hi The_DL,

According the knowledge base article to follow, you should contact Isilon Support immediately.The article states that the alert means that the cluster encountered an allocation error and manual intervention is needed.

453986 : OneFS: Event Notification: Allocation error detected: code:

 https://support.emc.com/kb/453986

I would recommend opening a Severity 1 service request. You can open a service request here:

https://support.emc.com/servicecenter/contactEMC/