I answered this question on Quora, but moderation deleted it, I guess because it references SiCortex, which has been shut down since 2009.
I am afraid I may be guilty of a little bit of pride here.
My information is also dated.
In 2007, the 5832 core 972 node SiCortex SC5832 could boot and be ready to run jobs in 7 minutes if the system support processor linux server was already running. From power off it would take about 9 or 10 minutes, with the extra time taken for the SSP to boot.
At the time, we had heard horror stories about clusters taking “hours” to boot, such that sysadmins were very reluctant to update software because it would take so long.
Earlier, in 2004 when we started the company, John Mucci asked me and the software team how long it was going to take to boot, and we said “5 minutes” to considerable eyebrow raising from people with more experience. Honestly we were guessing, but we couldn’t think of reasons why it should take longer.
Fast forward two years and we had to deliver. The machine was 36 boards, each with 27 6-core nodes and a little embedded Coldfire processor called the module support processor. The 972 nodes had no storage at all, so we had to boot over JTAG and load small ramdisk images. Then we had to initialize the high speed network, NFS mount the real root filesystem, and bring up the job control system. After a couple months of heroic efforts, we got it down to 7 minutes.
This was extraordinary in the industry, but we still got a lot of good natured razzing from the rest of the company for missing our 5 minute estimate.
To the software team, the most amusing part of the whole affair was that the hardware and software proved so reliable that we had several systems in the field with uptime over a year. With uptime like that it doesn’t really matter whether it takes 5 minutes to boot or 7 minutes or an hour for that matter.
Installation generally was a one-day affair. Here’s a video: SiCortex @ Argonne