Japan Exchange Group, Inc.

Tokyo Stock Exchange did not lose an entire trading day on 1 October 2020 merely because one memory card failed. The card failed inside a redundant shared-disk device; the configured standby did not take over; market-data and market-control functions shared that dependency; and the exchange had no rehearsed, industry-wide way to reconcile accepted orders and restart fairly after an abnormal network cut-off. The incident therefore tested much more than hardware reliability. It tested whether an exchange, its parent, its principal technology vendor and connected market participants could prove continuity when nominal redundancy did not behave as expected.