Can any one tell me why all environment fall if we lost one domain storage?

In my company we have many NFS storages and if just one going down, been rebooted, all host fail. 

What we realized, I do not know if it is true, is if one host can´t communicate with the storage it will be rebooted or if the use of memory is too high it will be rebooted too.

 

Are those two impressions real?

Best regards