Multiple brokerages, most famously Merrill Lynch, had both, primary datacenters and safes containing daily backup tapes in the WTC. There were unknown dependenc

Multiple brokerages, most famously Merrill Lynch, had both, primary datacenters and safes containing daily backup tapes in the WTC. There were unknown dependencies and backup systems that had been presumed to be independent did not work. Some secondary datacenters were in adjacent buildings also damaged by the attack. It had been assumed, given the extra protections put in place after the prior bombing, that the WTC was as safe as it gets so some firms had primary and secondary datacenters in different towers or different floors of the WTC. Multiple safes were plucked out and databases of customer positions were restored during the week the stock markets were closed. Getting these safes and the tapes out was given priority despite everything else going on because if the databases had not been brought back on line, there would have been absolute chaos in the markets. Immediately after the attack, exchanges moved their datacenter operations to sites in NJ about 80 miles apart and both exchanges and large brokerages setup backup datacenters in Delaware, far enough away to be unaffected by a thermonuclear blast hitting New York. I believe, prior to 2001 only JP Morgan (pre-Chase acquisition JP Morgan) had backup datacenters in Delaware but there may have been one or two others.