On the vger.kernel.org outage

I'd guess the subscriber lists (as used by the mailing list software) are on the array. It's
also necessary to write messages to disk during delivery because there are recipients whose
mail servers won't respond before it's necessary to acknowledge the messages from the senders,
but the subscriber lists are the reason you'd need data stored previously to have the mailing
lists work (aside from the eventual delivery of messages that were in progress when the array
crashed).