HP D5970A - NetServer - LCII Installation And Configuration Manual page 141

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. Table 2-2 in
Chapter 2 describes RAID levels for logical drives that 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.
Read Policy: The three Read policies for HP NetRAID are:
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.
Normal: This policy does not use the read-ahead memory caching feature.
This policy is efficient when most of the data reads are random.
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 logical drive.
Rebuild Rate: The speed at which the rebuild operation proceeds. Each adapter
is assigned a rebuild rate, which specifies the percentage of CPU resources to be
devoted to rebuild operations.
Reconstruct: The act of remaking a logical drive after changing RAID levels.
Redundancy: See RAID Levels
SCSI Channel: The HP NetRAID Series adapters control the disk drives via
SCSI-2 buses called "channels" over which the system transfers data in Fast-and-
Wide, Ultra SCSI, or Ultra-2 SCSI mode. Each HP NetRAID adapter can control
up to three SCSI channels. Each HP NetRAID-1 adapter can control one SCSI
channel.
Glossary
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