Disabling Alarm

Assuming you are talking about the LSI PERC controller's alarm, you would hit crtl+m during POST when you see it on the screen. At the management menu, go to 'Objects', 'Adapter' and then to 'Alarm Control'.

Couple of things to note, if you disable the alarm if there is ever a drive failure, the alarm will not sound and you may never know about it, unless you have Array Manager or Server Administrator installed and you check it. If it is sounding right now, you may want to take a look at the 'Physical Drive' menu under 'Objects' to see how the drives are doing.