HP LH4r Integrated HP NetRaid Controller Configuration Guide - Page 14

Hot Spares, Logical Drives

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Chapter 2 RAID Overview Arrays can combine disk drives that are all on one channel, or they can combine disk drives from one or two different channels. Hot Spares A hot spare is a powered-on, stand-by disk drive that is ready for use should another disk drive fail. When a disk fails, the HP NetRAID firmware can automatically rebuild the data from the failed disk onto the hot spare. The system administrator can then replace the failed disk and designate the replacement as the new hot spare disk. Until a rebuild occurs, a hot spare does not contain user data. There are two types of hot spares: • A global hot spare is used if a disk in any array fails. • A dedicated hot spare is reserved for use by a single array. Logical Drives The term "logical drive" refers to a virtual drive which is assigned some portion of the total capacity of an array. For example, if you have an array of disk drives with a total capacity of 80 GB, you can create a logical drive with a total capacity of 20 GB within that array. Logical drives can take three forms: • A logical drive can use all of the storage capacity of one array. In Figure 2-3, Logical Drive LD0 uses all storage capacity in Array A0. • A logical drive can use less than the available storage capacity of one array. In Figure 2-3, Logical Drive LD1 occupies only a part of Array A1. • A logical drive can span arrays by spreading across two, three, or four different arrays. In Figure 2-3, Logical Drive LD2 spans Arrays A1 and A2. 8

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Chapter 2
RAID Overview
8
Arrays can combine disk drives that are all on one channel, or they can combine
disk drives from one or two different channels.
Hot Spares
A hot spare is a powered-on, stand-by disk drive that is ready for use should
another disk drive fail. When a disk fails, the HP NetRAID firmware can
automatically rebuild the data from the failed disk onto the hot spare. The system
administrator can then replace the failed disk and designate the replacement as
the new hot spare disk. Until a rebuild occurs, a hot spare does
not
contain user
data.
There are two types of hot spares:
•
A global hot spare is used if a disk in any array fails.
•
A dedicated hot spare is reserved for use by a single array.
Logical Drives
The term "logical drive" refers to a virtual drive which is assigned some portion
of the total capacity of an array. For example, if you have an array of disk drives
with a total capacity of 80 GB, you can create a logical drive with a total capacity
of 20 GB within that array.
Logical drives can take three forms:
•
A logical drive can use all of the storage capacity of one array. In Figure
2-3, Logical Drive LD0 uses all storage capacity in Array A0.
•
A logical drive can use less than the available storage capacity of one
array. In Figure 2-3, Logical Drive LD1 occupies only a part of Array A1.
•
A logical drive can span arrays by spreading across two, three, or four
different arrays. In Figure 2-3, Logical Drive LD2 spans Arrays
A1 and A2.