On Dec 31, 2014, at 11:00 AM, m.roth@5-cent.us wrote:

Warren Young wrote:

...

How many single computers have to be up 24/7?

A hundred or more, here, individual servers, 24x7.

I’m more interested in a percentage than absolute values.

And I’m only interested in boxes that simply cannot go down for a bit of maintenance every now and then.

As counterexamples, DNS, NTP, and SMTP servers are out, because these protocols were explicitly designed to cope with short temporary outages.

Home directory servers, backup servers, compute nodes, some of which have jobs that run for days, or a week or two, and that's not counting the clusters that do the same... and mostly dump the data to home or project directories.

That’s all possible to work around.

Home servers: SAN design points the way.

Backup servers: Ditto if you mean home directory mirrors. If you mean hot failover nodes in a cluster, I already pointed out that clusters let you upgrade via temporary partitioning.

Compute nodes: I didn’t ask how many boxes you have that share the same 9/5/180 usage pattern of our customers. I asked how many you have that must run 24/7/365 or Bad Things happen. When a job that’s been running for 2 weeks finishes, there’s your maintenance window. Take it if you need it, let it go if you don’t.