How to detect the hard disk down immdeiately

[袁盛东]

Hello everyone:
         I use a hard disk as a storage node ,for example: tahoe in /storage folder,then mount /dev/sdb1 /storage ,then start the node I can see a green node in the web page,then I pull the hard disk to simulate the hard disk is broken down.but on the web page,I still see the node is green ,I want it turn red immediately to show the disk is broken down ,How can I do ? 
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