IBM 86655RY Hardware Maintenance Manual - Page 222

The array specifies which drives to include in the striping of data. Each array is subdivided into one or more logical drives. The logical drives specify the following: • The number and size of the physical drives as seen by the operating system. The operating system sees each defined logical drive as a physical drive. • The RAID level. When a logical drive is defined, its ServeRAID level (0, 1, or 5) is also defined. low-level format The writing of track and sector control information on the disk so that a computer system can store data in and subsequently retrieve data from the disk. mapping The establishing of correspondences between a given logical structure and a given physical structure. MB Megabyte; equal to approximately 1 000 000 bytes. menu-driven Concerning application software allowing user to select operations from one or more menus without entering keyboard commands. mirroring The process of writing the same data to two disk units within the same auxiliary storage pool (disk array) at the same time. The two disk units become a mirrored pair, allowing the system to continue when one of the mirrored units fails. non-volatile random access memory (NVRAM) Random access memory that retains its contents after electrical power is shut off. NVRAM Non-volatile random access memory. OFL Offline, a good drive that replaces a defunct drive in a RAID level-1 or level-5 array. This drive is associated with the array but does not contain any data. Drive status remains OFL during the rebuild phase. OKY Good functional state. The ServeRAID adapter's logical drive state in which all drives in the array are online and fully operational. ONL Online, a drive that ServeRAID adapter detects as installed, operational, and configured into an array appear as this state. overlap To perform an operation at the same time another operation is being performed; for example, to perform input/output operations while instructions are being executed by the processing unit. parity The state of being odd or even used as the basis of a method of detecting errors in binary-coded data. parity bit A binary digit appended to a group of binary digits to make the sum of all the digits, including the appended binary digit, either odd or even as preestablished. PFA The firmware of a hard drive uses algorithms to track the error rates on the drive. The drive alerts the user with a Predictive Failure Analysis (PFA) alert via the and Netfinity Director when degradation of drive performance (read/write errors) is detected. When a PFA alert occurs, physical replacement of the drive is recommended. 212 Hardware Maintenance Manual: Netfinity 7600 - Type 8665 Models 1RY, 2RY