The provision of multiple interchangeable components to perform a single function in order to cope with failures and errors, e.g. the setup of more power supplies to reduce the risk of failure of the entire system in case one of them fails.
Distributed Redundant UPS systems is a redundancy setup with three or more UPS where one serves as backup for the others in case one of them fails. There are 3 types of design and you can learn more here.
Distribution Redundancy is a type of redundancy setup in which the power distribution, not the power source, is redundant, using multiple rack PDUs. Distribution redundancy does not provide as much security as the full redundancy setup at power source level (Distributed Redundant UPS systems), because even if a server is connected to different Rack PDUs, the UPS remains the single point of failure. In the system, you can come across these variations: DN and DN+1, see these explained in the text below.
You may come across these terms in connection with power redundancy in the system:
- N: No redundancy.
- N+1: One UPS with one redundant power module (also referred to as internal redundancy in the UPS Power properties page). If the UPS fails, there is no redundant UPS serving as backup, but if one of the power modules inside the UPS fails, the redundant module ensures that the UPS still has full capacity. In other words, the spare power is at least equal to the capacity of one system module.
- 2N: Two UPS where one serves as backup for the other in case one of them fails. One UPS is referred to as A feed and the other as B feed.
- 2N+1: This is a combination of N+1 and 2N for combined external and internal redundancy, both one redundant UPS and one redundant power module inside both UPS.
- DN: This is a combination of D (distribution redundancy*) and N (above). For this type of redundancy, the power distribution is redundant but there is no redundancy on the UPS level. Therefore, you are still vulnerable to failure on the power supply. *In this case, distribution redundancy is referring to rack PDU redundancy, not UPS level redundancy.
- DN+1: This is a combination of D (distribution redundancy*) and N+1 (above). For this type of redundancy, the power distribution is redundant and there is internal redundancy on the UPS level (one UPS with one redundant power module).