Novell LINUX ENTERPRISE SERVER 11 - STORAGE ADMINISTRATION GUIDE 2-23-2010 Administration Manual page 94

"Near Layout" on page 95
"Far Layout" on page 95
Comparing the Complex RAID10 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 10-5
Feature
Number of devices
Component devices
Striping
Multiple copies of data
Hot spare devices
Number of Replicas in the mdadm RAID10
When configuring an mdadm RAID10 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 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.
94 SLES 11: Storage Administration Guide
Complex vs. Nested RAID 10
mdadm RAID10 Option
Allows an even or odd number of
component devices
Managed as a single RAID
device
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.
Two or more copies, up to the
number of devices in the array
A single spare can service all
component devices
Nested RAID 10 (1+0)
Requires an even number of
component devices
Manage as a nested RAID device
Striping occurs consecutively
across component devices
Copies on each mirrored
segment
Configure a spare for each
underlying mirrored array, or
configure a spare to serve a
spare group that serves all
mirrors.