Nitman,  That is correct, the Raid 5 requires at least 3 drives. With the size decrease, that is due to the Parity. The Raid 5 has striped blocks, and distributed parity. That means that the parity runs across, and is stored on,  all the drives. Unlike the Raid 3 that had completely separate drives that stored the parity. So essentially when you configure the array, the parity will be an equal % of the drives installed. So a 3 drive, a 1/3 of the space is designated to parity. 4 drives a 1/4 of each drive is used, and so on. The reason this is done is so that if any single drive is failed, then then remaining drives have the complete information across the remaining drives. Thus making the array redundant to a single drive failure. The raid 1 is basically a mirror, to where both drives have the same data, so if one fails, all the data is maintained.  Let me know if this helps.
Dear all, I'm sorry for the rather long question this is. I wonder if someone can help me understand how our system of hard drives and servers are setup. Our main server is a Poweredge 2950 with five physical hard drives. Three in a Raid 5 setup and the two others on Raid 1. The virtual Raid 1 drive size is 1.86 Tb. That matches what Open Manage Server Administrator says that the physical disks are two drives with each 1.86 Tb. The Raid 5 size is 930 Gb and OMSA says it is three drives of each 465 Gb. Do I understand correctly that in a Raid 5 configuration three drives are needed but the size is only made up of two drives? If not, where is the other 465 Gb gone?  Thanks, Magnus
Understanding our server system