Servers with hot swappable drive bays are always handy. However, things can turn ugly if the SCSI controller doesn’t like a new drive when it is inserted. You may end up with these errors in your dmesg output: The errors show that the SCSI bus is having issues bringing the new drive online, and it won’t be seen by the OS until the SCSI controller is pleased. You can force the controller to re-scan the drives attached to it, and this should correct the problem: