Adaptec 5325301638 Administration Guide - Page 45

RAIDs would configure one of the drives as a hot spare. The following table summarizes the advantages and disadvantages of each type of RAID: Comparative Advantages of RAID Types Features RAID 0 RAID 1 RAID 5 Data Loss Risk Write Access Speeds Usable Capacity Disks Required Supports Hot Spares Highest Fastest Highest 1 or more No Lowest Slower Lowest 2 or more Yes Low Faster High 3 or more Yes RAID Groups Two RAIDs can be grouped together to neatly resolve a number of capacity issues. For example, a volume on one RAID nearing full utilization can be expanded using spare capacity on another RAID. The ability to grow volumes beyond the capacity of a single RAID allows administrators to expand a volume without reconfiguring RAIDs and allows users to continue working as usual with no interruption. Consider the following scenarios: • Adding a Snap Disk Expansion Array - In a common scenario, a Snap Server 4500 configured as a RAID 5 is nearing full utilization. The administrator decides to add a Snap Disk 10 expansion array, which comes preconfigured as a RAID 5. The administrator groups the RAID from the expansion array with the existing RAID on the 4500, and then expands the size of the original volumes using the new storage from the expansion array. • Adapting to Unforeseen Requirements - A Snap Server 14000 is originally configured by an administrator with two separate RAIDs, each with its own hot spare. Usage on the first RAID is higher than expected and lower on the second RAID. By combining the RAIDs, the administrator can expand the volume from the first raid using the capacity of the second. Local and Global Hot Spares A hot spare is a disk drive that can automatically replace a damaged drive in a RAID 1 or 5. Designating a disk drive as a hot spare helps ensure that data is available at all times. If one disk drive in a RAID fails or is not operating properly, the RAID Chapter 4 Storage Configuration & Expansion 31