HP LH4r Installation and configuration of the HP NetRAID, NetRAID-1 and NetRAI - Page 22

Hot Spare, Logical Drive

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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 two or three different channels. Hot Spare 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 adapter's 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 on the adapter fails. • A dedicated hot spare is reserved for use by a single array. Logical Drive 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. 14

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Chapter 2
RAID Overview
14
Arrays can combine disk drives that are all on one channel, or they can combine
disk drives from two or three different channels.
Hot Spare
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 adapter's 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 on the adapter fails.
•
A dedicated hot spare is reserved for use by a single array.
Logical Drive
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.