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Create a clone from the system alert.
Go into the Alert configuration, find the alert and cerate a clone from this alert. This will open the alert definition dialog from the selected alert.Expand title picture for this step ... 
Add a new filter condition to the alert.
First Add the object type, second add the filter condition
Use the add button to expand the pre filter statement of the alert
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Click into Object type and select the object type SVC Cluster
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Add the filter condition with the button Add filter condition
- NOT ( device_model_name contains "FS900" OR device_model_name contains "FS840" ) into the text field or do the job with the button
- (1) select attribute - you find it in Attribute → Type->Device model
- Comparator - use contains
- Value - enter 920
Select Add condition and complete the condition
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Save the modified selection
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- Move the new selection as first selection with Drag&Drop
Check the path it has to be BVQ / SVC Cluster / SVC VDisk
Change the name of the alert (1) and and save it with the button bottom right of the form (2)
You will be asked whether you want to disable the predefined alert rule with saving the new rule and the answer should be yesExpand title picture for this step ... 