A colleague of mine worked for EMC in the 90s and early 2000s, and has some insane stories around 9/11. They drove him down to New York later that week, where he joined a team of federal reserve, SEC, DTCC, and army combat engineers whose job was to locate at ground zero the remains of a few EMC storage arrays and pull the drives. These frames had transaction records on them that had to be recovered in order to open the markets on the 17th. The issue was that the primary and secondary replicas were in data centers in building 1 and 2. No one had ever considered that both buildings could be destroyed simultaneously. Shortly thereafter, three-site mirroring with an asynchronous leg out-of-metro became a mandatory standard for all mission critical banking data.
If I remember correctly all they needed was the last 30 seconds or so of missing data, and they were able to recover it off the drives in the symmetrix lab up in Hopkinton.
EMC sales types told us that the EMC method of using "vault" disks--disks that cached writes for the rest of the SAN--saved the bacon of various companies that lost power in lower Manhattan that day.
