Computer Hardware User Manual

52 IBM Certification Study Guide AIX HACMP
mirroring rootvg in order to avoid the impact of the failover time involved in a
node failure. In terms of maximizing availability, this technique is just as valid
for increasing the availability of a cluster as it is for increasing single-system
availability.
The following procedure contains information that will enable you to mirror
the root volume group (rootvg), using the advanced functions of the Logical
Volume Manager (LVM). It contains the steps required to:
• Mirror all the file systems in rootvg.
• Create an additional boot logical volume (blv).
• Modify the bootlist to contain all boot devices.
You may mirror logical volumes in the rootvg in the same way as any AIX
logical volume may be mirrored, either once (two copies), or twice (three
copies). The following procedure is designed for mirroring rootvg to a second
disk only. Upon completion of these steps, your system will remain available if
one of the disks in rootvg fails, and will even automatically boot from an
alternate disk drive, if necessary.
If the dump device is mirrored, you may not be able to capture the dump
image from a crash or the dump image may be corrupted. The design of LVM
prevents mirrored writes of the dump device. Only one of the mirrors will
receive the dump image. Depending on the boot sequence and disk
availability after a crash, the dump will be in one of the following three states:
1. Not available
2. Available and not corrupted
3. Available and corrupted
State (1) will always be a possibility. If the user prefers to prevent the risk of
encountering State (3), then the user must create a non-mirrored logical
volume (that is not hd6) and set the dump device to this non-mirrored logical
volume.
In AIX 4.2.1, two new LVM commands were introduced:
mirrorvg and
unmirrorvg. These two commands where introduced to simplify mirroring or
unmirroring of the entire contents of a volume group. The commands will
detect if the entity to be mirrored or unmirrored is rootvg, and will give slightly
different completion messages based on the type of volume group.The
mirrorvg command does the equivalent of Procedure steps (2), (3), and (4).
The
mirrorvg command takes dump devices and paging devices into account.
If the dump devices are also the paging device, the logical volume will be