Administration Guide

Using mirrored root volume groups

You can set mirroring options and initiate mirroring on nodes that have already been installed, or you can set mirroring options and have mirroring initiated during installation of a node. You can also suspend mirroring. The mirroring options that you can set using the spchvgobj command for a given root volume group are: how many copies you want (2 or 3), which disks to use, and whether quorum is to be on or off.

In general, quorum should be turned off in a mirrored environment and turned on in an environment without mirroring. Quorum is turned on by default during node installation unless you specify -q false with the spchvgobj command before installation when you first set the mirroring options. After installation, the -q flag has no affect except when you initiate or suspend mirroring. To turn quorum off on a node that is already installed, specify -q false with the spchvgobj command when you set the mirroring options before you initiate mirroring. If you want to turn quorum on again, specify -q true with the spchvgobj command before you suspend mirroring.

To initiate mirroring of a root volume group on a node that is already installed, use the spmirrorvg command after you set mirroring options. To suspend mirroring, use the spunmirrorvg command. These commands also issue the bosboot and bootlist commands on the nodes to create the necessary boot records and to manage the list of bootable devices. If the state of quorum changes on a node as a result of initiating or suspending mirroring, a warning message appears prompting you to reboot the node for the new state of quorum to take effect. See the book PSSP: Command and Technical Reference for details of how to use these commands.

Examples of some typical tasks follow.

Installing a node without mirroring

This sample task installs a node without mirroring and sets the lppsource_name attribute for the node.

To install node 3 without mirroring and set lppsource_name to aix432, do the following:

1. Change the volume group rootvg to use the lpp source name aix432 on node 3.

   spchvgobj -v aix432 -r rootvg -l 3
   

2. Change the node 3 bootp response to install.

   spbootins -r install -l 3 -s yes
   

3. Network boot the node.

   nodecond 1 3
   

Installing a node with mirroring

This is a sample task to install a node with mirroring established from the start.

To install node 5 with two disks for mirroring with the original copy on hdisk0 and a mirror image on hdisk1, do the following:

1. Change the rootvg volume group information for node 5 to indicate that you want two copies using physical disks hdisk0 and hdisk1, and you want quorum turned off (quorum is turned on by default during installation).

   spchvgobj -h hdisk0,hdisk1 -c 2 -r rootvg -q false -l 5
   

2. Change the node 5 bootp response to install.

   spbootins -r install -l 5 -s yes
   

3. Network boot the node.

   nodecond 1 5
   

Initiating mirroring on a node already installed without it

This sample task extends the root volume group on a node and starts mirroring. The node has already been installed but without mirroring.

To create a mirror of hdisk0 on hdisk1 for node 3, do the following:

1. Change the rootvg volume group on node 3 to have two copies using physical disks hdisk0 and hdisk1, and indicate that you want quorum turned off.

   spchvgobj -h hdisk0,hdisk1 -c 2 -r rootvg -q false -l 3
   

2. Start mirroring on node 3.

   spmirrorvg -l 3
   

3. Reboot node 3 if the state of quorum changes, as indicated by the warning message.

   cshutdown -r -N 3
   

Restrictions to mirroring

The following is a list of mirroring restrictions:

• The nodes to be mirrored and the control workstation must be running AIX 4.3.2 or later and PSSP 3.1 or later.
• Mirroring is not performed for dump logical devices.
• AIX supports only double or triple mirroring (the original and one or two more copies of the original).
• AIX does not support mirroring of striped logical volumes.
• Mirroring support does not extend to the control workstation from these commands.
• PSSP supports turning quorum on or off only when mirroring is initiated or suspended.