The following recommendations apply to the operating system disks that constitute the rootvg volume group:
The rootvg comprises the operating system related files, the default logical volumes, and the paging space only. This keeps the backup of AIX (mksysb) small and makes the move to another hardware or operating system easier.
The sizing of the rootvg should provide comfortable space for the /, /tmp, and /var file systems, as these file systems may have a serious impact on an application if they are full.
The daily or hourly effort of monitoring these file systems can be reduced drastically by extending the file systems to reasonable sizes. For example, a full /tmp can also cause pending print jobs, backup failures, or a failing installp command. As a result, overhasty actions to correct the failure may imply other mistakes. Assuming a price of $5000 for a 36 GB disk; the cost for a 100 MB /tmp directory is about $15. This assumes less than five minutes of unplanned downtime, which can be caused by a full /tmp directory or an accidental mistake when removing temporary files.
For a reliable environment, the rootvg has to be mirrored in a manner similar to application data volume groups. The mirroring should include the paging space; otherwise, a failing rootvg disk, including paging space, will cause a system crash.
If we assume two existing disks (hdisk0/hdisk1) in the rootvg and two added disks (hdisk2/hdisk3), the mirroring of a rootvg is managed by these steps:
1. Place all the volumes, including the paging spaces, on the first two disks (hdisk0/hdisk1) according to your requirements.
2. Create the logical volume copies with an exact identical mapping using the command:
/usr/sbin/mirrorvg -m rootvg hdisk2 hdisk3
3. Find out the disks on which the boot logical volume (blv=hd5) copies reside with the command:
/usr/sbin/lslv -l hd5
We assume that hdisk0/hdisk2 is the result.
4. Check the contiguity of the hd5 volume. The hd5 volume must reside within the first 4 GB of the disk. You can check this by issuing the command:
/usr/sbin/lslv -m hd5
The PP number multiplied with the PP size must be below 4 GB.
5. Write the boot record and the boot logical volume on the new disk using the command:
/usr/bin/bosboot -a -d /dev/hdisk2
6. Add the new disk to the bootlist using the command:
/usr/bin/bootlist -m normal -o hdisk0 hdisk2
7. Reboot the system to activate the changed quorum settings.
