On Dec 31, 2014, at 11:00 AM, m.roth at 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.