LSI MegaRAID SCSI 320-2 RAID Controller Series 518 User Manual download pdf (Page 148)

C-6 Glossary

RAID Redundant Array of Independent Disks. A data storage method in which

data, along with parity information, is distributed among two or more hard

disks (called an array) to improve performance and reliability. A RAID

disk subsystem improves I/O performance on a server using only a single

drive. The RAID array appears to the host server as a single storage unit.

I/O is expedited because several disks can be accessed simultaneously.

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 5 requires at least three

physical drives. RAID levels 10 and 50 result when logical drives span

arrays. RAID 10 results when a RAID 1 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; in

Windows NT, it is Power Console Plus. If a RAID 1 array is being

converted to a RAID 0 array, 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-Ahead A 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 it is not as effective

when accessing random data.

Ready State A condition in which a workable disk 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, or 5

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.

Reconstruct The act of remaking a logical drive after changing RAID levels or adding

a physical drive to an existing array.

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LSI MegaRAID SCSI 320-2 RAID Controller Series 518 User Manual Page 148