IBM 86655RY Hardware Maintenance Manual - Page 220

• By reading every file on the disk, the backup process forces the disk and the controller to discover any sector media errors and to correct them, greatly decreasing the likelihood of the rebuild failures described in the previous section. If weekly tape backups are performed, data scrubbing is still recommended to detect and correct sector media errors in non-data areas of the drives. If a sector media error has not been discovered and an array rebuild fails as described previously, a full tape backup can then be performed to minimize data loss. The tape backup saves all files except for the one containing the damaged sector. The drives can then be restored from the configuration disk and synchronized, forcing the remapping of bad sectors. The data can then be restored. The files that were contained on the damaged sector would then have to be restored from a prior backup. Automatic Data scrubbing: Automatic data scrubbing continuously reads all sectors of all logical drives in the background while the system is running. If a defective sector is found, it is automatically repaired. The advantage to this procedure, when used in addition to tape backups, is that data scrubbing examines unallocated sectors of the drive, in addition to those that have been allocated, that is, data areas protected by a tape backup. If any sector media errors are found during this process, they are corrected at the disk level using disk ECC information, if possible, or at the array level using RAID parity information, if necessary. Automatic data scrubbing is enabled by defaults. Note: You do not need to synchronize RAID level-0 or 1 logical drives before storing data. Data scrubbing continuously reads all sectors of RAID-1 and RAID-5 logical drives in the background while the system is running. If a defective sector is found, it is automatically repaired. As a result of this feature, you no longer have to synchronize logical drives on a weekly basis. Acronyms, terms, and definitions Acronyms and terms are listed in alphabetical order in the following table. array An arrangement of data in one or more dimensions: a list, a table, or a multidimensional arrangement of items. In the ServeRAID environment, data is striped across multiple physical hard drives. The array is defined as the set of hard drives included in the data striping. block A string of data elements recorded or transmitted in a unit. The elements may be characters, words, or physical records. byte A string of eight bits that is treated as a unit, and that represents a character. cache memory A special buffer storage, smaller and faster than main storage, that is used to hold a copy of instructions and data in main storage that are likely to be needed next by the processor, and that have been obtained automatically from main storage. CDR CD-ROM CRT Critical DASD Direct access storage device. Data Scrubbing The process that forces all data sectors in a logical drive to be accessed so that sector media errors are identified and corrected at the disk level using disk ECC information, if possible, or at the array level using ServeRAID parity information, if necessary. For a high level of data protection, perform data scrubbing weekly. 210 Hardware Maintenance Manual: Netfinity 7600 - Type 8665 Models 1RY, 2RY