After I add one 750GB disk in 4x750GB-disk raid-5 array and rebuild it, I can see 3000GB of space in raid console:
http://img143.imageshack.us/img143/290/raid1kj1.jpg
But in Open-E window I see only 2095.48GB
http://img156.imageshack.us/img156/9571/dss1og4.jpg
How can I fix this?