HP LH4r Installation and configuration of the HP NetRAID, NetRAID-1 and NetRAI - Page 43

Chapter 4 Planning • Consider what RAID levels you will need. ◊ Different RAID levels require different minimum numbers of physical drives. For example, RAID 1 requires exactly two physical drives, RAID levels 3 and 5 require at least three physical drives, and arrays with only one physical drive must be assigned RAID 0. ◊ Different RAID levels reserve different amounts of capacity to provide redundancy. • A single array can be divided into a maximum of eight logical drives. • A single HP NetRAID Series adapter can control a maximum of eight logical drives. • If you want to use the online capacity expansion feature later on, logical drives cannot span arrays and there must be only one logical drive per array. • If you want one logical drive to span two or more arrays: ◊ Spanned arrays must be numbered consecutively. ◊ Spanned arrays must contain the same number of disk drives per array. ◊ Although each physical drive in an array must have the same capacity, one logical drive can span two or more arrays of different capacities. For example, one array might contain three drives of 1 GB each, and the second array might contain three drives of 5 GB each. One logical drive can span both of these arrays. ◊ Spanned arrays must be controlled by the same adapter. As you plan your arrays, it might help to sketch your configuration. See Figures 4-2 and 4-3 for examples. In Figure 4-2, Logical Drive 2 (labeled "LD2") spans arrays A1 and A2, occupying space in both. Each array of physical drives is on a separate channel. 35