RAID 1 capacity problem

Hello

I have problem with Adaptec 2100S SCSI controller and 2 Seagate ST373307LW hard disks drives 73 GB /U320.

These disk are present in controller setup (CTRL+A) like 68 GB hard drives, but when I create RAID 1 its capacity is always 34700 MB (I expected 68 GB).

In the other case when i create RAID 0 between these 2 disks its capacity is only 68 GB (expected 136 GB)

In the JBOD mode these disks can work as 34700 MB only disk not 68 GB.

Where is the problem: contoller, disks, cnfiguration?
I want to build RAID 1 with 68 GB capacity. What should I do?

Thank you for every suggestion.

Mark