HP StorageWorks 4000s NAS 4000s and 9000s Administration Guide - Page 61

Storage Management Overview Online Spares Further protection against data loss can be achieved by assigning an online spare (or hot spare) to any configuration except RAID 0. This hard drive contains no data and is contained within the same storage sub system as the other drives in the array. When a hard drive in the array fails, the controller can then automatically rebuild information that was originally on the failed drive onto the online spare. This quickly restores the system to full RAID level fault tolerance protection. However, unless RAID ADG is being used, which can support two drive failures in an array, in the unlikely event that a third drive in the array should fail while data is being rewritten to the spare, the logical drive will still fail. Physical Storage Best Practices Minimally, choosing the best disk carving strategy includes the following policies: ■ Analyze current corporate and departmental structure. ■ Analyze the current file server structure and environment. ■ Plan properly to ensure the best configuration and use of storage. - Determine the desired priority of fault tolerance, performance, and storage capacity. - Use the determined priority of system characteristics to determine the optimal striping policy and RAID level. ■ Include the appropriate number of physical drives in the arrays to create LUNs of desired sizes. Logical Storage Elements Overview Logical Storage elements consist of those components that translate the physical storage elements to the file system elements as presented in Figure 23. The NAS server utilizes the WebUI to manage the various types of disk presented to the file system. The WebUI has two types of LUN presentation, basic disk and dynamic disk. Each of these types of disk has special features that enable different types of management. Through the use of basic disks, primary partitions or extended partitions may be created. Partitions can only encompass one LUN. Through the use of dynamic disks, volumes can be created that span multiple LUNS. The WebUI can be used to convert disks to dynamic and back to basic, and manage the volumes residing on dynamic disks. Other options include the ability to delete, extend, mirror, and repair these elements. The sections below briefly discuss each of these types of representations and the considerations that need to be observed. More detailed information regarding the WebUI for disk management activities can be obtained in the Disk Management Chapter. Partitions Partitions exist as either Primary Partitions or Extended Partitions and can be composed of only one Basic disk no larger than 2 TB. Basic disks can also only contain up to four primary partitions, or three primary partitions and one extended partition. In addition, the partitions on them cannot be extended beyond the limits of a single LUN. Extended partitions allow the user to create multiple logical drives. These partitions or logical disks can be assigned drive letters NAS 4000s and 9000s Administration Guide 61