If any nodes except the node used to run BACKUP are booted
during the backup operations described in this appendix, your cluster
will become partitioned, where nodes in the existing cluster divide
into two or more independent clusters. This condition can cause
data file corruption.
In addition, these backup environments do not restrict your
use of DCL commands to the BACKUP command only, which further increases
your risk of accidentally destroying or corrupting data on a disk.
Therefore, to avoid jeopardizing the integrity of your data in any
way, HP recommends that you shut down the entire OpenVMS Cluster
system before you back up your system disk.
HP OpenVMS Alpha Version 7.3-2 Upgrade and Installation... 
Backing Up and Restoring the System Disk
