security and piece of mind

My sister and I both purchased external hard drives to back up an ever increasing number of digital pictures...We both take a lot of pictures and with a high quality camera that uses a lot of memory. I use mine mainly for backup but also to help clear out files from my computer drive...I also back the pictures up on cd or dvd so I feel they will be there when I want or need them...The 250g Lacie external drive (my sis had to top me with a 500g) works fine but I do not keep it plugged into the USB or turned on except when I am using it...