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ECS provides strong consistency, requiring I/O requests to check with the owner before responding. Because of this requirement, access to some buckets and objects might be temporarily disrupted if a site is inaccessible.
Site outages can occur for different durations:
To detect temporary site outages, federated sites establish a heartbeat between sites. The default is 15 minutes. If the heartbeat is lost between sites for a sustained period of time:
As an example, in a three-site configuration, if Sites 2 and 3 both lose network connectivity to Site 1 for a sustained period of time, ECS will mark Site 1 as temporarily failed.
When a federated site is failed, system availability can be maintained by directing access to other federated systems. During the site-wide failure, the geo-replicated data owned by the unavailable site becomes temporarily unavailable. The following factors determine the duration that the data remains unavailable:
The site failure can either be temporary or permanent. A temporary site outage means the site can be brought back online and is typically caused by power outages or loss of networking between sites. A permanent site outage is when the entire system is unrecoverable, such as from a lab fire. Only an administrator can determine if a site outage is permanent and instigate recovery operations.