[ale] Linux Cluster Server Room

[Bjorn Dittmer-Roche]

On Mon, 19 Apr 2004, Dow Hurst wrote:

> I understand your philosophy here but have a question?  What if the
> calculations are long and costly to restart?  Shouldn't I look at the value of
> spent computation that might have to be done over if I lose power?  The code I
> am most concerned about running on the cluster may or may not be
> checkpointable.  I think it might be, but I know my users and they won't want
> power to be an issue with predicting when their jobs will finish. ;-)
>
> Are Best UPS better performing than Tripplite or APC?  I have experience with
> Tripplite, APC, and Leibert so far and never used Best.  I like the toughness
> and quality of the enclosure of the APC and Leibert.  I like the quality of
> all three.  I like the performance and cost of APC and Tripplite.  Tripplite's
> cases or enclosures on the low end aren't as nice as APC, but when you get the
> high UPSes they have nice rack enclosures.  Performance wise, I haven't been
> able to tell a difference between the two.  Heat production leans toward APC
> producing less overall.

I have not used the high end from APC or tripplite, but I had a friend
who's school got _struck_ _by_ _lightning_ and their tripplite UPS ended
up totally black and charred but it still worked and none of the machines
were damaged at all! The tripplite support team was thrilled and sent them
a new one at no charge. IIRC that was a midrange model.

BestPower's high end is incredible. There is some fundamental difference
between them and their competitors, in that BestPower makes use of a giant
transformer. I can't recall the exact result of this, but I think it
has to do with making the power smoother and improves handling of
brownouts and overvoltages.

They also have hella huge batteries. IIRC, our runtime was something like
two hours! (granted it was just a sun E450, some raids, a tape drive and
two x86 servers, but still...)

> What do you mean by getting the wrong power factor conversion? Do you mean
> getting 120v at 60Hz vs 220v at 60Hz on the output outlets?

"Power factor" has to do with the relationship in phase between voltage
and current, which is altered by any electrical components which are
highly reactive (like capacitors) or inductive (like coils). When using
equipment that alters the phase of the power, you must make sure that the
source of the power can handle the phase changes. (When customers use lots
of power, power companies charge not just for "real" power but also for
this "reactive power".)

Anyway, some equipment alters the phase of the current relative to the
voltage and you need to make sure the device supplying the power
(especially if it's a lot of power) can handle it.

All this is usually nothing to worry about as long as your supplier knows
the UPS is for computers. You can learn more by googling things like
"power factor" "reactive power"  and maybe even "three phase power",
"electrical phase" or "power phase", but like I said, just tell your
supplier what it's for and hopefully they won't screw up (like ours did.)

	bjorn