ALSR Configurations

An automated local site recovery (ALSR) configuration connects two physical machines in two separate sites. It is a disaster-tolerant deployment that maintains hardware redundancy as well as redundancy of physical computer rooms and the buildings containing them. Because of the geographic separation, an ALSR configuration requires careful planning of component placement and more complex networking topologies. For ALSR configurations, Stratus strongly recommends that you use the quorum service because an ALSR configuration exposes the A-Link networks to other potential failure scenarios. (ALSR configurations are not available to systems configured with one node.)

Meeting Network Requirements lists the requirements for networks in a ALSR configuration.

ALSR and Quorum Service

In an ALSR configuration, configure two quorum-service computers in compliance with the best practices recommended for quorum deployment (see Quorum Servers and Locating and Creating the Quorum Server). In any ALSR configuration, a preferred quorum-service computer is located in a third facility, and an alternate is located in a fourth site (or carefully placed in the third). The networks are interconnected.

Quorum-service computers should be as isolated as possible. If both must be placed in a common (third) site, make sure that they do not depend on common power sources.

Physical connectivity between an ztC Edge PM and the quorum-service computers must not route through the other PM's site.

Placing a quorum-service computer in the same site as one of the ztC Edge PMs ensures data integrity. However, some site failures may then require that the VMs be shut down until manually recovered.

The management network physically connects the ztC Edge PMs and the quorum-service computers. For this to work properly, you must configure each ztC Edge PM to use a different gateway to reach the quorum-service computers. If the two PMs use the same gateway to reach the quorum-service computers, data integrity is ensured during failures. However, some site failures may then require that the VMs be shut down until manually recovered.