Understanding The Mdadm Raid10 - Novell LINUX ENTERPRISE SERVER 10 - STORAGE ADMINISTRATION GUIDE FOR EVMS Administration Manual

7.3.1 Understanding the mdadm RAID10

In mdadm, the RAID10 level creates a single complex software RAID that combines features of
both RAID 0 (striping) and RAID 1 (mirroring). Multiple copies of all data blocks are arranged on
multiple drives following a striping discipline. Component devices should be the same size.
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
Feature
Number of devices
Component devices
Striping
Multiple copies of data
Hot spare devices
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
80 SLES 10 Storage Administration Guide for EVMS
"Comparison of RAID10 Option and Nested RAID 10 (1+0)" on page 80
"Number of Replicas in the mdadm RAID10" on page 80
"Number of Devices in the mdadm RAID10" on page 80
"Near Layout" on page 81
"Far Layout" on page 81
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.