About Logical Devices
A logical device lets you run one application instance (either ASA or Firepower Threat Defense) and also one optional decorator application (Radware DefensePro) to form a service chain .
When you add a logical device, you also define the application instance type and version, assign interfaces, and configure bootstrap settings that are pushed to the application configuration.
For the Firepower 9300, you must install the same application instance type (ASA or FTD) on all modules in the chassis; different types are not supported at this time. Note that modules can run different versions of an application instance type.
Standalone and Clustered Logical Devices
You can add the following logical device types:
Standalone—A standalone logical device operates as a standalone unit or as a unit in a High Availability pair.
Cluster—A clustered logical device lets you group multiple units together, providing all the convenience of a single device (management, integration into a network) while achieving the increased throughput and redundancy of multiple devices. Multiple module devices, like the Firepower 9300, support intra-chassis clustering. For the Firepower 9300, all three module application instances belong to a single logical device.
For the Firepower 9300, all modules must belong to the cluster. You cannot create a standalone logical device on one security module and then create a cluster using the remaining 2 security modules.