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 14-2shows 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

Disk Group

Site B

 

 

Volume V

Plex P1

 

Plex P2

 

Plex P3

 

Plex P4

 

 

 

 

 

 

 

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.