RAID 6

Hi all

We wanted to have 100 TB storage of RAID 6- out of which 70 TB with 3TB sata disks  and 30 TB with 600GB SAS disks.

Please clarify how many disks of 3 TB and how many disks of 30 TB is required for usable 100 TB with best performance of RAID 6.

Also please clarify part no: 403-BBDC related to MD3620f dual controller with 4 GB cache each.

Please clarify me ..its urgent

thanks