Re: The server was ok - after all, it could handle a failed a disk.
The article has extra text indicating the real timeline, which you have missed. Here is the timeline in its original form.
Day 1: Hard drive 1 fails, server stays up.
Somewhere in the middle, probably day 2 morning: Team inserts a new drive into array to recover.
Day 2 noon: Server team leaves for party, desktop team comes in to manage things, repair still in progress.
Day 2 afternoon: Hard drive 2 fails, server goes down.
For the desktop team, it was the first thing they saw with the server, as they didn't put in the new drive. Since Sam was on that team, that was his first knowledge. It was the second drive that did it. The article has the events out of order, and the clue was "Eventually it transpired that [...] the day previously." We're getting the events from Sam's point of view, and he wasn't there from the beginning.