[Beowulf] Re:UPS system for Linux cluster

[John Bushnell]

David Mathog wrote:
> vlad at geociencias.unam.mx wrote:
>  
>   
>> I have a linux cluster and need to purchase a UPS system.
>> The total expected current consumption will be 240 amps. At 120 V this
>> would require a 30 kVA UPS system.
>> However, I see that 30 kVA systems have a limitation for the input
>> current. For example, this 30 kVA system
>> (http://www.provantage.com/tripp-lite-su30k3-3xr5~7TRPL1Q9.htm) allows
>> only 90 amps as input
>> current. I am a bit confused here, and I need some advice on what UPS
>> system I should look for.
>>     
>
> Do you really need a UPS for the whole cluster?
>
> In many instances it is good enough to put a UPS on the master node and
> just use surge suppressors on the compute nodes.  The up side being that
> only a small and relatively inexpensive UPS is required.  The down side
> being of course that any power failure will break ongoing calculations.
>  However, if your work can be check pointed a power failure will only
> wipe out the work since the last check point.  If your power is
> reasonably reliable, this is a reasonable way to save a lot of money.
> Also, unless you are also buying a generator, a whole cluster UPS will
> only buy you limited up time during a power failure, so you may well
> lose the calculation  despite the large UPS.
>
> Regards,
>
> David Mathog
>
>   
Another reason for not having UPS power for an entire cluster is 
cooling.  In our server room, if we lose regular power, we lose our 
large AC units as well.  So we need to be careful what we keep plugged 
into our emergency power circuits (a relatively tiny amount of 
equipment).  Having an entire stack of nodes churning away during a  
power outage would kill us pretty quickly.

  - John