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176 IBM Certification Study Guide AIX HACMP
• Cluster nodes should be running the same HACMP maintenance levels.
There might be incompatibilities between various maintenance levels of
HACMP, so you must ensure that consistent levels are maintained across
all cluster nodes. The cluster must be taken down to update the
maintenance levels.
8.7 Backup Strategies
HACMP software masks hardware failures in clustered RISC System/6000
environments by quickly switching over to backup machines or other
redundant components. However, installing HACMP is not a substitute for
having a formal backup and recovery procedure.
In general, a backup of user and system data is kept in case data is
accidentally removed or in case of a disk failure. A formal backup process is
really an insurance policy. You invest in the technology and time to back up
systems so that, in the event of a problem, you can quickly rebuild the
system.
Since system and application backups are preferably done during periods of
no usage (for instance, in the middle of the night), many installations
implement an automated backup procedure using the AIX cron facility. While
this is a very good procedure, the HACMP cluster environment presents
some special challenges. The problem is, you never know which machine has
your application data online, so you need to ensure that exactly the node that
has a resource online will initiate the backup of data.
It isn’t actually important which of the several backup commands you are
using, what is important is the strategy. For the features and/or restrictions of
backup commands like
tar, cpio, dd or backup, refer to the
AIX Commands
Reference Version 4.3
,
SBOF-1877.
8.7.1 Split-Mirror Backups
No file system can be safely backed up while update activity is occurring. If
you are going to have any assurance as to which updates are on the backup
and which updates are not, you need to be able to demark exactly where the
backup was made. Therefore, it may be difficult to do a good backup on
systems that have applications or data that must be online continuously or
offline for only a very short time. In some installations, the time required to do
a full backup to an archival device, or even to another, might be longer than
the availability requirements of the application will allow it to be offline. The
mirroring capability of the AIX Logical Volume Manager (LVM) can be used to
address this issue.