The devices all have their own cooling fans and the rack will allow airflow from front to back. Here's a labeled photo. The "cloud" servers are 3 machines that act as around 20 "virtual" computers. The Network Attached Storage (NAS) box right above cloud1 & 2 hold all the storage for the virtual machines plus the shared storage for all the desktop/laptops in the house. Each machine is hooked to its own UPS box so it can be notified of a power outage, but the house has a generator so the UPS's only have to last about 15 seconds before the generator kicks in. The firewall box is a general computer I built with the pfSense software to act as the firewall. The KVM box above it allows all these computers to share one keyboard/mouse/monitor. The ethernet switch is the main hub where everything connects together (the rest of the house plugs in here as well). Camera is a box some cameras plug into and become available on the network. VOIP ties the house phones into the network. WLAN is one of the 3 wireless network points. Backup is the temporary external drive acting as a 3rd failure protection for the NAS (which can survive a single drive failure on its own - the most valuable data on the NAS (family photos) are also backed up to Amazon Glacier in case the house burns down or gets hit by a meteor. Since that backup drive isn't going to be big enough for long I'm going to make the cloud3 machine into a new NAS box which will use spare hard drives to backup the main NAS, then I'll just get another thin virtualization server.
But the real activity is on the 3 cloud machines. In various virtual machines I'm running a PBX system, web server, database, Jenkins continuous build system, a home automation system I wrote, virtual Windows Home Server 2011 machine which does full backups of all the Windows machines in the house. I even run the email for my domains, DHCP and DNS (both internal and external) servers in virtual machines as well as network health monitoring and monitoring/controlling the generator. The home automation "brain" I wrote controls various lighting and security features of the house and provides useful information (weather, customized news, other stuff).
The fact that I know how to do all this stuff is how I pay for my Festool habit.