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432 Administering sites and remote mirrors
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 190). 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
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 A Site B
Disk Group
Plex P3 Plex P4Plex P1 Plex P2
Volume V