2 hard disks management

Hello,
Friends

kindly suggest me that
1. My system has two harddisks one is in which i am working regularly

2. hard disks i have some delicated erp sofware,

Now i can make 1 master and other as slave disk
But master disk when I will in net it damages the slave hard disk

What i want is there is any external switch which can be connected to switch the power supplly if so plz give your valuble suggestion