Tieto , one of the larger outsourcing companies in the Nordic countries had a major datacenter crash about two years. This was caused by a storage area network (SAN) turning corrupt during an upgrade. For redundancy they had a second storage set but that did not help as it also went corrupt doing mirroring in real time.
When changing recovery strategy to restore it was found out the backup was not restoreable due to upgraded OS (or something like that).
Service for several large organisation was down for almost a week.
The problems for BA at Heathrow reminds me about this as both the wide outage as well as the long time before being operational again are similar.