Shared Disk (SD) secondary

SD secondary servers share disk space — except temporary dbspaces — with the primary server. This is typically done through a network-based clustered file system. Adding a new SD secondary to a cluster is very easy and can be done in a few seconds once the shared disk is prepared. Because SD secondary nodes leverage the primary's disks and can be brought up easily and quickly, they are well-suited for scale-out scenarios. In SD secondary servers checkpoints are synchronized. This means a checkpoint at the primary server completes only after the checkpoint at the SD server completes. SD secondary supports committed read and committed read last committed isolation levels as well as dirty read. An SD secondary can be promoted to a primary server with one single command: onmode -d make primary <name of SD server>. Because an SD secondary server is so close to the primary (in other words, it shares the same disk), it is often the best type of server to initially fail over to if the primary should encounter a problem.