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Automating Unmirror and Remirror for Solaris Volume Manager Volumes

Victor Feng, November 2007

Introduction

When performing operating system or application system upgrades or changes, a cautious system administrator unmirrors the volumes so there are two independent systems. Then, if the upgrades or changes go wrong in one system, the second system can kick in right away. After finishing the upgrades or changes, the system administrator needs to recreate mirrors for the system.

The unmirror script provided with this article automates the following tasks:

1. Unmirror the volumes so that one system is split into two systems.
2. Prepare the second system to be ready for use in the event of a failure.
3. Re-create the mirrors for the first system as they existed before.

Here's the source code for the unmirror script. Please rename it so it has a .sh extension instead of a .txt extension.

Note: The unmirror script and the following procedure were tested with the Solaris 10 Operating System, but they should also work with previous Solaris versions. The unmirror script unmirrors and remirrors Solaris Volume Manager based RAID 1, 0+1 volumes for UFS file systems. The script leaves other RAID type volumes and simple partitions alone.

How to Use the unmirror Script

1. As root, run the following command:

# ./unmirror

2. Perform your system upgrades or changes.

3. If the upgrades or changes succeed, as root, run the following command:

# ./remirror

Or, instead, if the upgrades or changes fail, boot from the root disk of the second system.

Explanation of the unmirror Script

The unmirror script generates three additional scripts:

• unmirror_cont
• remirror
• remirror_cont

The specific contents of the unmirror_cont, remirror, and remirror_cont scripts vary based on your volumes.

Here's a sample scenario:

# metastat -p
d3 -m d13 d23 1
d13 1 2 c1t2d0s6 c1t3d0s6 -i 32b
d23 1 2 c1t2d0s7 c1t3d0s7 -i 32b
d1 -m d11 d21 1
d11 1 1 c1t2d0s1
d21 1 1 c1t3d0s1
d0 -m d10 d20 1
d10 1 1 c1t2d0s0
d20 1 1 c1t3d0s0
d4 2 1 c1t2d0s4 \
	 1 c1t3d0s4

Here's an example of the unmirror_cont script for this scenario:

Here's an example of the remirror script for this scenario:

Here's an example of the remirror_cont script for this scenario:

After detaching submirrors, the unmirror script creates a symbolic link file in /etc/rc3.d for unmirror_cont and reboots the system so that the link file continues to finish the unmirroring after the reboot. After finishing upgrades or changes, you can then run the remirror script to re-create the mirrors that existed before on the system. The remirror script creates a symbolic link file in /etc/rc3.d for remirror_cont before rebooting the system, and the link file continues to finish the mirroring after the reboot.

The unmirror script unmirrors and remirrors Solaris Volume Manager based RAID 1, 0+1 volumes. The file system for the volumes is UFS. The script leaves other RAID type volumes and simple partitions in the system alone.

The unmirror script does not run the metaclear submirror command, and it does not remove the metadatabase, because it does not need to re-create the submirror and the metadatabase when it remirrors the volumes.

The core task of the unmirror script is to read md.cf row by row. In the previous example, each RAID 1 volume has three rows, starting with first row with -m. A row counter (rows) is set to 2 when the first row is found. The counter is reduced by 1 after the next row is read. When the row counter is 1, the Unmirror_PrepareRemirror function is called to unmirror the system and to continue to prepare the other three scripts. The program also determines whether a submirror is a physical partition or a volume (for example, RAID 0). If both the second and the third parameters are 1, the submirror is a physical partition.

Note: Throughout the whole unmirroring process, the vfstab2 file is updated so that it will be used as /etc/vfstab for the second system.

Unless otherwise licensed, code in all technical manuals herein (including articles, FAQs, samples) is provided under this License.