Hello,

Calendar Server can be (and is, in rare instances) deployed in a high-availability (HA) configuration, which can also be used to scale. Check out the following document, which identifies the important parts of a multi-server configuration.

Removing all single points of failure would require implementing HA / redundancy for each of the items listed in that document, which is beyond the scope of our documentation, but should be a familiar process for anybody who has ever implemented HA.

XMLDirectoryService is probably the most scalable directory service we support, due to its simplicity. If it meets your needs, I can’t think of a reason to switch away from it.

-dre