HP NetRAID 1Si Controller User Manual
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Glossary
147
RAID Levels: A style of redundancy applied to a particular logical drive. It may
increase the performance of the logical drive, and it may decrease its usable
capacity. Each logical drive must have a RAID level assigned to it.
RAID levels 0, 1, 3, and 5 are for logical drives that occupy a single array (do not
span arrays). Briefly,
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RAID 0 has no redundancy. It requires one or more physical drives.
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RAID 1 has mirrored redundancy. It requires two physical drives in an
array.
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RAID 3 has parity redundancy with a dedicated parity disk. It requires
three or more physical drives in an array.
•
RAID 5 has parity redundancy distributed over all the disks in the array. It
requires three or more physical drives in an array.
RAID levels 10, 30, and 50 result when logical drives span arrays.
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RAID 10 results when a RAID 1 logical drive spans arrays.
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RAID 30 results when a RAID 3 logical drive spans arrays.
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RAID 50 results when a RAID 5 logical drive spans arrays.
Read Policy: The three Read policies for HP NetRAID are:
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Read-Ahead: This is a memory caching ability that tells the adapter to
read sequentially ahead of requested data and cache the further data in
memory, anticipating that the further data will be requested. Read-Ahead
supplies sequential data faster, but is not as effective when accessing
random data.
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Normal: This policy does not use the read-ahead memory caching feature.
This policy is efficient when most of the data reads are random.
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Adaptive: Adaptive policy causes the read-ahead feature to be used if the
last two disk accesses were in sequential sectors.
Ready State: A condition in which a workable hard drive is neither online nor a
hot spare, and therefore 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, 5,
10, 30, or 50 array to a replacement disk. A disk rebuild normally occurs without
interruption of application access to data stored on the array virtual disk.