Veritas Volume Manager 5.1 SP1 Administrator"s Guide (5900-1506, April 2011)

Figure 14-2 shows an example of a site-consistent volume with two plexes
configured at each of two sites.
Figure 14-2
Site-consistent volume with two plexes at each of two sites
Site A Site B
Disk group
Volume V
Plex
P1
Plex P2 Plex P3
Plex
P4
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.
Although not shown in this figure, DCO log volumes are also mirrored across the
sites, and disk group configuration copies are distributed across the sites.
Site consistency means that the data in the plexes for a volume must be consistent
at each site. The site consistency of a volume is ensured by detaching a site when
its last complete plex fails at that site. If a site fails, all its plexes are detached and
the site is said to be detached. If site consistency is not on, only the plex that fails
is detached. The remaining volumes and their plexes on that site are not detached.
To enhance read performance, VxVM will service reads from the plexes at the
local site where an application is running if the siteread read policy is set on a
volume. Writes are written to plexes at all sites.
Figure 14-3 shows a configuration with remote storage only that is also supported.
467Administering sites and remote mirrors
About sites and remote mirrors