Can you add another drive to a raid 5?

Do you mean add a disk to an already existing raid array, or can you have more than the 3 disk minimum? Either way, yes you can, though I find if you already have raid 5 setup with 3 disks and you want to add another one you are better off starting it all over from scratch again. As far as I can remember, I may be wrong, but all the disks have to be equal. You cant have a three 40GB drives at 5400rpm and then add in a new drive off 120GB at 7200rpms. And are you using a raid 5 hardware option or software option. If your doing it via hardware you may need to upgrade your disk controller. And dont forget your going to have convert your new disk when you get it. Drives are usually basic, raid5 wont work on a basic disk. Actually you can add disparaging disks to an array but you'll only get the capacity of the existing disks in the array - therefore in the above setup, adding the 120Gb@7200rpm wouldn't give you the capacity of the 120Gb, only an additional 40Gb.