For enhanced availability, VMSclusters support the use of dual-ported disks connected to two machines or storage controllers simultaneously.
At that stage, clustering required specialised communications hardware, as well as some major changes to low-level subsystems in the VMS operating system.
In addition, MSCP packets were easily transported over the CI allowing remote access to storage devices.
In 1986, DEC added VAXclustering support to their MicroVAX minicomputers, running over Ethernet instead of special-purpose hardware.
While not giving the high-availability advantages of the CI hardware, these Local Area VAXclusters (LAVc) provided an attractive expansion path for buyers of low-end minicomputers.
Unlike many other clustering solutions, VMScluster offers transparent and fully distributed read-write with record-level locking, which means that the same disk and even the same file can be accessed by several cluster nodes at once; the locking occurs only at the level of a single record of a file, which would usually be one line of text or a single record in a database.
Cluster connections can span upwards of 500 miles (800 km), allowing member nodes to be located in different buildings on an office campus, or in different cities.
This allows cluster configurations to continue to provide application and data access while a subset of the member nodes are upgraded to newer software versions.