Question : Problem: How much space do I get using raid 5 with 3 drives?

I am about to purchase and IBM XSeries server for a client.  It has been my understanding that in a RAID 5 configuration using 3 identical drives, the usable amount of drive space available for data is equal to the size of one drive.  IBM is telling me that  it is equal to 2 drives.  What's up.  Can you clear this up for me?

Answer : Problem: How much space do I get using raid 5 with 3 drives?

Ooops... forget about the 75%.... I was thinking of another EE.com question.

Total array size would be equal to the capacity of one drive multiplied by the number of drives minus 1...  (Size of 1 drive) * (Number of drives -1) = Total capacity.