Glossary, Continued

RAID Levels A style of redundancy applied to a logical drive. It can increase the performance of the logical drive and can decrease usable capacity. Each logical drive must have a RAID level assigned to it. The RAID level drive requirements are: RAID 0 requires one or more physical drives, RAID 1 requires exactly two physical drives, RAID 3 requires at least three physical drives, RAID 5 requires at least three physical drives. RAID levels 10, 30, and 50 result when logical drives span arrays. RAID 10 results when a RAID 1 logical drive spans arrays. RAID 30 results when a RAID 3 logical drive spans arrays. RAID 50 results when a RAID 5 logical drive spans arrays.

RAID Migration RAID migration is used to move between optimal RAID levels or to change from a degraded redundant logical drive to an optimal RAID 0. In Novell, the utility used for RAID migration is MEGAMGR and in Windows NT its Power Console. If a RAID 1 is being converted to a RAID 0, instead of performing RAID migration, one drive can be removed and the other reconfigured on the controller as a RAID 0. This is due to the same data being written to each drive.

Read-AheadA memory caching capability in some adapters that allows them to read sequentially ahead of requested data and store the additional data in cache memory, anticipating that the additional data will be needed soon. Read-Ahead supplies sequential data faster, but is not as effective when accessing random data.

Ready State A condition in which a workable hard drive is neither online nor a hot spare and is available to add to an array or to designate as a hot spare.

Rebuild The regeneration of all data from a failed disk in a RAID level 1, 3, 4, 5, or 6 array to a replacement disk. A disk rebuild normally occurs without interruption of application access to data stored on the array virtual disk.

Rebuild Rate The percentage of CPU resources devoted to rebuilding.

Cont’d

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