Back in my network engineer days at Nortel, uptime was something that was seen as vitally important. With the growth of the business pre-dotcomBUST, the production lines and the servers managing them needed to be up and serving 24×7.
24x7x365 was a very hard thing to measure, never mind achieve in pre-2000 information systems. In the end my overseers and bosses had to reconcile the need for maintenance and upgrades with the 24x7x365 myth and the uptime was achieved though we were able to maintain a very reasonable schedule – so reasonable in fact that the business was able to celebrate when we relinquished some of our regular maintenance windows.
But the message was clear, uptime was the most important metric.