Even thought the 6th disk is 300GB in size and the usable space on that drive is ~266GB you cannot just add that space to the first 5 drives' capacity. The 6th drive's usable capacity will shrink automatically since you are creating a RAID Group that contains a disk from the first 5 drives.  Even if you create a RAID Group with drives 0_0_4,0_0_5,0_0_6,0_0_7,0_0_8 you will still only get 1032GB of usable capacity because one of the drives in that RAID Group is a vault drive
A RAID 5 group uses the five 300 GB disks 0_0_0 to 0_0_4 for a total user capacity of 825 GB. A customer expands the RAID group with an additional 300 GB disk. What will the total user space in GB be on completion? and why ?  1 )    1032   2 )    1093  3)     990             It is wrong  4 )    1125           It is wrong
Raid calculation