Planned outages Before looking at the differences between internal- and external-managed environments, we  look at the similarities between the two of them.  As shown in Figure 1-3, an update or upgrade of the underlying hardware or firmware (FW)  can be hidden from the user. The outage period is the time that it takes to move to the new  hardware and FW environment. In both cases, you can make the change on the backup  system while the application is still running on the production environment. From a planning  point of view, you need a second downtime to move back to the production environment.  Make the same hardware and FW changes on the production environment before you move  the application back to it.  In an internal-managed environment, the update of the operating system and application can  be hidden from the user because you have multiple independent installations. As described in  1.1.1, “General concepts” on page 3, the update can be made on the backup system while  the application is still running on the current environment, as shown in Figure 1-3. In an external-managed environment, you need a longer downtime to do an update to the  operating systems or application because you have only one operating system and one  installation of the application. You cannot hide the whole time that is needed to make the  updates from the user, as shown in Figure 1-3. As listed in Figure 1-4 on page 6, the unexpected outage of the hardware, operating system,  or application can in some cases be covered in a similar way for both architectures. However,  if data corruption occurs, the outage can be different. Because the data in both cases is available only once, the effect of data corruption is the  same. This is the worst case scenario because it requires a restore of your data from your  backup media. This restoration can take a long time, and your recovery point might be old. The outage time also can differ based on the cause of the outage. An outage of one of the  components is detected much faster than data corruption on one of the components. The  outage detection time does not differ much regarding the selected architecture.  Unplanned outages Figure 1-3 Software and hardware maintenance-dependent action times Chapter 1. Introduction to high availability and disaster recovery  5