LSI MegaRAID Express 500 User Manual
Page 141
Glossary
127
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-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 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