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

Figure 14-3
Example of a two-site configuration with remote storage only
Cluster or
standalone
system
Fibre
Channel
switch
Fibre Channel
switch
Disk enclosures Disk enclosures
Site A
Metropolitan
or wide area
network link
(Fibre Channel
or DWDM)
Site B
About site-based allocation
Site-based allocation policies are enforced by default in a site-configured disk
group. Site-based allocation requires that each volume has at least one plex at
each site that is configured in the disk group. When a new volume is created in a
site-configured disk group, the allsites attribute set to on, by default. The
allsites attribute indicates that the volume must have at least one plex on each
configured site in the disk group. For new volumes, the read policy is set to
siteread by default.
If mirroring across sites is not required, or is not possible (as is the case for RAID-5
volumes), specify the allsites=off attribute to the vxassist command. If sites
are configured in the disk group, a plex will always be confined to a site and will
not span across sites. This enforcement cannot be overridden.
Before adding a new site to a disk group, be sure to meet the following
requirements:
■ Disks from the site being added (site tagged) are present or added to the disk
group.
■ Each existing volume with allsites set in the disk group must have at least
one plex at the site being added. If this condition is not met, the command to
Administering sites and remote mirrors
About sites and remote mirrors
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