RAID 1: breaking mirrors and rebuilding drives, 4th Edition

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Introduction
This paper explains the two methods for safely breaking a RAID 1 or RAID 1(+0) mirror and
rebuilding drives in RAID 1(+0) volumes using HP Smart Array controllers. The first method uses the
HP Array Configuration Utility (ACU) split mirror feature. You can only use this method while a server
is offline and it requires an HP Smart Array Advanced Pack (SAAP) license. You can also use a
manual method with any Smart Array controller.
You may need to break a RAID 1(+0) mirror to create a backup of the RAID volume or to increase
capacity.
Breaking the mirror lets you remove half of the mirrored drives and use them as a backup. You might
want this backup to protect against failure or for troubleshooting software configurations. You can
reestablish the mirror later by replacing the backup drives with new drives. The controller will
automatically rebuild the new drives and restore fault tolerance.
Breaking the mirror lets you replace half of the drives in a RAID 1 or RAID 1(+0) array with larger
capacity drives and rebuild the new drives. Afterwards, you can replace the remaining half of the
original drives with another set of new drives and then rebuild again. Once this is complete, you can
use the Array Configuration Utility (ACU) to increase the logical drive size or to configure additional
volumes.
Splitting a mirrored array using the Array Configuration
Utility
This function splits an array of RAID 1 or RAID 1(+0) logical drives into two identical new arrays
consisting of RAID 0 logical drives. This is different from the manual method, in which the volumes
keep their RAID 1 or RAID 1(+0) configuration after you split the mirror. Note that using the ACU
does not require you to split all the arrays attached to the controller at the same time.
The ACU will show the Split Mirror task as an available option only under all of the following
conditions:
• Both the ACU version and the selected controller support the action.
• The server is offline.
• You have installed the applicable Smart Array Advanced Pack keys.
Complete the following steps to split a mirrored array using the ACU:
1. After taking the server offline, insert the CD or bootable USB drive that contains the ACU (typically
SmartStart) into an appropriate media drive.
2. Restart the system, booting to the CD or bootable USB drive.
3. From the Maintenance Operation menu, select the HP ACU.
4. In the selection panel, select Array Configuration and Diagnostics.
5. In the Configuration drop down menu, select the applicable controller.
6. Highlight or select the desired logical drive.
7. In the Available Tasks panel, click Split Mirrored Array.
8. Click OK.
9. You will see both logical drives in the Systems and Devices tree after ACU has finished splitting the
array.