Novell LINUX ENTERPRISE SERVER 10 SP3 - ARCHITECTURE-SPECIFIC, Руководство администратора

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104 SLES 10 SP3: Storage Administration Guide
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“Number of Replicas in the mdadm RAID10” on page 104
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“Number of Devices in the mdadm RAID10” on page 104
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“Near Layout” on page 105
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“Far Layout” on page 105
Comparison of RAID10 Option and Nested RAID 10 (1+0)
The complex RAID 10 is similar in purpose to a nested RAID 10 (1+0), but differs in the following
ways:
Table 7-5
Complex vs. Nested RAID 10
Number of Replicas in the mdadm RAID10
When configuring a RAID10-level array, you must specify the number of replicas of each data block
that are required. The default number of replicas is 2, but the value can be 2 to the number of devices
in the array.
Number of Devices in the mdadm RAID10
You must use at least as many component devices as the number of replicas you specify. However,
number of component devices in a RAID10-level array does not need to be a multiple of the number
of replicas of each data block. The effective storage size is the number of devices divided by the
number of replicas.
For example, if you specify 2 replicas for an array created with 5 component devices, a copy of each
block is stored on two different devices. The effective storage size for one copy of all data is 5/2 or
2.5 times the size of a component device.
Feature mdadm RAID10 Option Nested RAID 10 (1+0)
Number of devices Allows an even or odd number of
component devices Requires an even number of
component devices
Component devices Managed as a single RAID
device Manage as a nested RAID device
Striping Striping occurs in the near or far
layout on component devices.
The far layout provides sequential
read throughput that scales by
number of drives, rather than
number of RAID 1 pairs.
Striping occurs consecutively
across component devices
Multiple copies of data Two or more copies, up to the
number of devices in the array Copies on each mirrored
segment
Hot spare devices A single spare can service all
component devices Configure a spare for each
underlying mirrored array, or
configure a spare to serve a
spare group that serves all
mirrors.