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Managing Software RAIDs 6 and
1 0
10 with mdadm
This section describes how to create software RAID 6 and 10 devices, using the Multiple Devices
Administration (
mdadm(8)
tool provides the functionality of legacy programs
Section 10.1, "Creating a RAID 6," on page 89
Section 10.2, "Creating Nested RAID 10 Devices with mdadm," on page 90
Section 10.3, "Creating a Complex RAID 10 with mdadm," on page 93
Section 10.4, "Creating a Degraded RAID Array," on page 96
10.1 Creating a RAID 6
Section 10.1.1, "Understanding RAID 6," on page 89
Section 10.1.2, "Creating a RAID 6," on page 90
10.1.1 Understanding RAID 6
RAID 6 is essentially an extension of RAID 5 that allows for additional fault tolerance by using a
second independent distributed parity scheme (dual parity). Even if two of the hard disk drives fail
during the data recovery process, the system continues to be operational, with no data loss.
RAID 6 provides for extremely high data fault tolerance by sustaining multiple simultaneous drive
failures. It handles the loss of any two devices without data loss. Accordingly, it requires N+2 drives
to store N drives worth of data. It requires a minimum of 4 devices.
The performance for RAID 6 is slightly lower but comparable to RAID 5 in normal mode and single
disk failure mode. It is very slow in dual disk failure mode.
Comparison of RAID 5 and RAID 6
Table 10-1
Feature
Number of devices
Parity
Performance
Fault-tolerance
) tool. You can also use
mdadm
mdtools
RAID 5
N+1, minimum of 3
Distributed, single
Medium impact on write and
rebuild
Failure of one component device
to create RAIDs 0, 1, 4, and 5. The
and
.
raidtools
RAID 6
N+2, minimum of 4
Distributed, dual
More impact on sequential write
than RAID 5
Failure of two component devices
Managing Software RAIDs 6 and 10 with mdadm
10
mdadm
89
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