Adding more CPUs & PSUs to an ES40 Alpha and retaining power resiliance

[Howard Anderson_2]

We need to add a third CPU to each of our 2 clustered ES40 systems running Tru64 Unix 4.0G (TruCluster 1.6).
At present we run 2 CPU's and 2 PSU's in each system. The 2 PSU's in each system are connected to 2 separate datacentre wide UPS systems.
Once each month one of these UPS systems is shutdown and restarted, to test power resiliance.
I know that I need a third PSU to retain resiliant power input to the ES40 with 3 or 4 CPU's. However, how do I connect the 6 power leads into the 2 UPS feeds ?
I do not want the powerfail test to cause a switchover of our clustered applications.
Has anyone had to solve this already ?

[Uwe Zessin]

Howard,
assume you connect server 1, PS1+2 to power 1 and PS3 to power 2. Server 2, PS1 to power 1 and PS2+3 to power 2. If you test power 1, then server 1 will fail and if you test power 2, then server 2 will fail.

If you connect the other way round, then you have just swapped which server will fail during which test.

You might try and move the application during a window of inactivity (if you have one) to the unaffected server before you run the test, but that means you have to move every week.

It looks to me that you need a third, independed power source to prevent a failover in all situations.

[Howard Anderson_2]

Uwe,

Many thanks for the quick response.
I had considered doing this form of wiring so that only one system is impacted at any one time, but as you say maybe I need a third UPS supply. Unfortunatly at present this is not an option from a datacentre wide point of view due to the huge cost involved.
I could look at using 2 small addional UPS systems, one connected to each machines third PSU on one side, and opposing datacentre wide UPS's on the other, to tide the systems over during the powerfail test.
The system is 24x7 available, but does have quieter periods of operation, so maybe we could switch prior to the test. I was hoping to avoid this, as we do not need to do so at the moment.
Regads,

Howard Anderson

[Blake Roberts · Accepted solution]

This is a fundamental flaw in the design of the ES40s, unfortunately. One other way around it is to put switching PDUs inside the cabinet. APC has an in-rack model which will do the switching between the redundant power feeds. These are usually used for single-corded servers, however it would work well for this scenario as well.

Hope this helps,
--Blake Roberts

[Hein van den Heuvel]

Folks interested in this topic may also want to check out:

http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=565089

Over there Dirk Bogaerts hints to a fast switching dual feed distribution unit.

fyi,
Hein.