IMAGINE that a communication link fails in a two-node CLUSTER. Both SERVERS may think the other one is down and begin servicing the resource that you want to be highly available. If this resource needs access to the shared FILE system on the SAN, you may end up with a situation where both servers try to write to the same file system at the same time. If you are using a file system like Ext3, XFS or Ext4, this will cause severe file system corruption. The STONITH device makes SURE that one of the servers is really shut down before a server can take over a resource from another. It does that by cutting the power to the server so it really is down. This sounds like a strange solution, but it's much better than having file system corruption.

Imagine that a communication link fails in a two-node cluster. Both servers may think the other one is down and begin servicing the resource that you want to be highly available. If this resource needs access to the shared file system on the SAN, you may end up with a situation where both servers try to write to the same file system at the same time. If you are using a file system like Ext3, XFS or Ext4, this will cause severe file system corruption. The STONITH device makes sure that one of the servers is really shut down before a server can take over a resource from another. It does that by cutting the power to the server so it really is down. This sounds like a strange solution, but it's much better than having file system corruption.