HP Surestore Disk Array FC60 HP SureStore E Disk Array 12H User's and Service - Page 83

Chapter 4. Concepts and Management This chapter describes in greater detail the concepts and management of the disk array, including features and hardware design of the disk array. This information will give you a better understanding of how the disk array operates, which should help you make some of the decisions involved in managing the disk array. Included is a very brief description of some of the basic concepts of disk array technology for those unfamiliar with disk arrays. If you would like to know more about disk arrays, many good articles have been published on the subject. Disk Arrays in Brief A disk array uses a group (or array) of disk drives connected to an array controller, which distributes (or stripes) data across the disks in the array. Disk array technology offers the potential to provide three important benefits: high availability, high performance, and cost-efficient data storage. Perhaps the most important feature of disk arrays is their ability to provide high availability, or protection against disk failure. This protection is achieved through the use of redundant information, which is used to reconstruct data that is lost when a disk fails. Disk arrays typically offer a variety of techniques for managing redundant information. These techniques are referred to as RAID levels. The RAID level used has a direct impact on the remaining two factors: performance and cost-efficient data storage. Although there are a number of different RAID levels, the only two we are concerned with here are RAID 0/1 and RAID 5. • RAID 0/1 - gives you data redundancy and good performance, but the performance is achieved by using a less efficient technique of storing redundant data called "mirroring." Mirroring maintains a backup copy of all data, so half of the disk space is consumed by redundant data. This results in a higher cost to store your data. • RAID 5 - provides data redundancy and improves cost-efficiency by using a more efficient method of storing redundant data. However, the storage method extracts a performance penalty for each write operation. This can impact system performance if your applications frequently update large amounts of data. 83 Concepts