Veritas Volume Manager 5.0 Administrator's Guide (September 2006)

424 Administering sites and remote mirrors
For more information about administering Extended Distance Clusters, see Designing
Disaster Tolerant High Availability Clusters (at http://docs.hp.com --> High Availability
--> Metrocluster).
If a disk group is configured across the storage at the sites, and inter-site communication is
disrupted, there is a possibility of a serial split brain condition arising if each site continues
to update the local disk group configuration copies (see “Handling conflicting
configuration copies” on page 182). VxVM provides mechanisms for dealing with the
serial split brain condition, monitoring the health of a remote mirror, and testing the
robustness of the cluster against various types of failure (also known as fire drill).
For applications and services to function correctly at a site when other sites have become
inaccessible, at least one complete plex of each volume must be configured at each site
(site-based allocation), and the consistency of the data in the plexes at each site must be
ensured (site consistency).
By tagging disks with site names, storage can be allocated from the correct location when
creating, resizing or relocating a volume, and when changing a volume’s layout.
Figure 14-2 shows an example of a site-consistent volume with two plexes configured at
each of two sites. The storage for plexes P1 and P2 is allocated storage that is tagged as
belonging to site A, and the storage for plexes P3 and P4 is allocated storage that is tagged
as belonging to site B.
Figure 14-2 Site-consistent volume with two plexes at each of two sites
Site A Site B
Disk Group
Plex P3 Plex P4Plex P1 Plex P2
Vo l u m e V