Serial Port
Serial Port

While pursuing the 100% virtual mark you once in a while run into trouble with legacy hardware where there is hardware directly attached to the physical server you are going to virtualize. If it is USB equipment you can use USB Anywhere devices to make it happen, but if it is serial port connected equipment it gets harder to tackle that issue.

For instance you want to virtualize a building management system server with reading equipment connected to the serial ports. Is that possible? Yes you can!

It is possible to use a Virtual Serial Port Concentrator, as for instance the Avocent ACS V6000, which is described in this KB article and as mentioned in the vSphere 5 documentation here.

By connecting physical serial ports over the network with a virtual machine you can break the dependency of the physical layer and the OS layer. By solving this puzzle you can protect the organization against legacy hardware failure  and/or from software that nobody knows how it is installed anymore.

You can set up virtual serial ports connections for vSphere virtual machines in several ways. The connection method that you select depends on the task that you need to accomplish. You can set up virtual serial ports to send data in the following ways:

Physical serial port on the hostSets the virtual machine to use a physical serial port on the host computer. This method is useful for using an external modem or a hand-held device in a virtual machine.
 
Output to fileSends output from the virtual serial port to a file on the host computer. This method is useful for capturing the data that a program running in the virtual machine sends to the virtual serial port.
 
Connect to a named pipeSets a direct connection between two virtual machines or a connection between a virtual machine and an application on the host computer. With this method, two virtual machines or a virtual machine and a process on the host can communicate as if they were physical machines connected by a serial cable. For example, you can use this option for remote debugging on a virtual machine.
 
Connect over the networkEnables a serial connection to and from a virtual machine’s serial port over the network. The Virtual Serial Port Concentrator (vSPC) aggregates traffic from multiple serial ports onto one management console. vSPC behavior is similar to physical serial port concentrators. Using a vSPC also allows network connections to a virtual machine’s serial ports to migrate seamlessly when you use vMotion to migrate the virtual machine.
 

Important I tried out an USB-to-Serial cable but that wont work, because serial ports connected through USB are not supported for serial port passthrough by VMware.