When content is uploaded to a site, the advanced storage
area selects the replicas to which to upload the content synchronously,
in the following priority order:
- Selects a single site-local replica (primary or secondary) with
preference for primary. However, if there is no primary designated
for the local site, it selects the secondary on the local site before
it selects a primary on a remote site.
- Until the desired number of synchronous replicas are met, continue
to select replicas in the following order:
- Local site primary replicas
- Remote site primary replicas
- Local site secondary replicas
- Remote site secondary replicas
- After this selection mechanism, if the required number of synchronous
replicas are not met, then fail the upload.
Any failure in the synchronous upload to any of the selected replicas
forces reevaluation of the replica priorities, and automatic failover
takes place. If the required number of replicas is achieved for synchronous
upload, the upload succeeds. All remaining replicas use the asynchronous
upload mechanism. Content is uploaded to all the replicas set on the
connections in the advanced storage area.