No subject

[bogus@does.not.exist.com ()]

degrade your
power estimates.  How much?  The real answer is the one I hate to
hear, 'it depends'.

At one place we went so far as to take one of each type of equipment,
and profile it
during normal 'spin up', after the 'plug was pulled', and even during
the power down event.
The best equipment I found to measure that was expensive, but it was
basically a recording scope
or meter that has a strip chart on it.  For single phase, you really
want to have a plot
of both the amps and volts, and if possible, a 'true RMS' value.  If
you don't have
electronic engineers on staff, I suggest outsourcing it.

You may be able to get specs for 'startup peak power usage' from your vendo=
r.
And you could add them all together.  The problem is you will not use as mu=
ch
of your capacity for power from each circuit.  You really can over
subscribe the power use if the
concurrent power use doesn't go over the real available power parameters.
(Think back to the Apollo 11 movie, they spent hours figuring out the
right sequence
to power on equipment to keep from blowing their last power cells.  A
geekly dramatic
part of the film)

Another frustrating thing is that all identical equipment doesn't have
the same power
profile.  Often similar, but due to variances in components, it never
seems to be 'the same'
when you need it to be. (A Murphy's law corrilary)

As noted before, switching power supplies are pretty good these days.
Apple went on the
bleeding edge and switchers built a reputation for being unreliable.
Over the years they
have become MUCH better, and don't display as much of the inrush
problem as there used
to be when equipment was put online (the initial buildup of magnetic
fields on power transformers
and initial charge of large filter capacitors were a real issue in
analog power supplies before
the switchers came along.  Analogs are still great, but heavy,
expensive (just think of the copper).

Disk drives still have some inrush issues because of the motors.  The
newer motors again are
much better and the drives are lower mass platters that help greatly.
The drives also monitor
speed digitally and control the motors much more precisely with lower
power electronics.
Fans have some of the same issues.

Other things you will find frustrating is that if you turn on and off
breakers, or
from just age, ... breakers wear out.  The don't fail suddenly most
often but they
reduce the amount of power they will pass before they blow.  Once a
breaker starts
that death march, you really want to have it replaced sooner rather than la=
ter.

Historically, large mainframes had to be powered up and down in sequence.  =
This
helped ensure the huge power inrush didn't shut down a data center (that se=
ems
even today to look like a major short circuit across grid power), and equip=
ment
had a chance to cool properly before all the power was cut off.  It
could take 10 mins
or more in some data centers once a shutdown command was entered and
acknowledged.

<war story>  If you remember
seeing a 'big red button' near the door exiting computer rooms in the
past, it was
'Emergency Power Off'.  We had a maid press that one night to 'get out
the door'.
It caused immediate drop of all power to the data center except for emergen=
cy
lights.  The quiet was deafening.  Maids were never allowed back in
the room, and
computer techs did all cleaning after that.  It took 6 months to get
rid of the last of the
thermal damage that was caused because things did not get turned off
in sequence,
fans didn't run till the equipment was 'sufficiently cool', etc.
Basically it cooked lots
of circuits in lots of different equipment.  Of course they add didn't
fail immediately,
some did, but most that did fail did so over the next several months.
This was at a major Oil company in Houston.

At the same facility, we were trying to save energy (yes, even oil companie=
s
try to save energy and money), so some of the 'building engineers' couldn't=
 see
why we needed to have any cooling towers running on weekends in the winter.
They turned them all off on Friday night after 5PM and it took to
about 9PM before
the mainframes failed with 'thermal faults'.  It was Monday before we deter=
mined
there had been a 'policy change', but the 'policy was changed again' due to=
 that
incident.  Our problem was we could have caught it earlier except we were
running a 'lights out' facility, and there was no one in the 'computer
room', all
the operators were down the hall in the 'operator and tape drive' room.  Th=
e
computer room only had non-hands on hardware (CPU, disk drives,
controllers, etc).
and in there the alarms had been going off for several hours we
finally determined.
We had 'extended enunciators' installed, basically an always on baby monito=
rs
so the operators could listen for alarms in the 'lights off' rooms.
</war story>

><> ... Jack
Whatever you do, work at it with all your heart... Colossians 3:23


On Thu, Oct 13, 2011 at 12:00 PM, Jerry Feldman <gaf at blu.org> wrote:
> One question I have is in planning. One day we received a shipment of abo=
ut
> 5 or 6 Intel systems from out Toronto office. We ordered a rack, switch, =
and
> a rack KVM. We initially plugged everything in to a wall outlet. ran fine
> until it tripped a breaker, and the breaker box was not in the computer
> room, but somewhere else on the floor where we had to call building
> management. All I knew that the wall outlets were NEMA 5-20. The solution=
 at
> that time was to take the two 6U monsters and plug them in to separate
> outlets in the ceiling. This worked for quite a while until my boss broug=
ht
> in a system he had at home (another 4U Intel whitebox). At that time I ha=
d a
> rack power strip, and the power strip popped a breaker, but the wall circ=
uit
> was fine. I then bought another strip to split the load. before all that =
I
> estimated our power usage by adding up the wattage on the power supplies
> (each was about 700W). Each wall outlet also went to a separate breaker. =
It
> was at this point when we were getting the HP ESX box and IT somewhat
> dictated that we get 2 240V outlets). Right now I am pulling about 15A (7=
 on
> one, 8 on the other). But, the critical factor is at takeoff, or when
> starting all the systems, such as after a power fail. You've got all your
> systems spinning up drives and fans. This is what we need to plan. So, I
> would need a rule of thumb that I can take the wattage of each power supp=
ly
> and figure out my maximum amps. Had I performed that calculation initiall=
y,
> I would have had fewer outages. I can't help when a truck, bus, or tree
> takes out the entire Riverside T station and us :-)
>
> On 10/13/2011 12:29 PM, Tom Metro wrote:
>>
>> Edward Ned Harvey wrote:
>>>
>>> Hold it. =A0P=3DVI is a DC rule. =A0Power is more complex in AC.
>>> What's the difference between VA and W?
>>>
>>> If you have inefficient power supplies, you might be overpaying 30%
>>> for power.
>>
>> You're referring to power factor:
>> http://en.wikipedia.org/wiki/Power_factor
>>
>> =A0 The power factor of an AC electric power system is defined as the
>> =A0 ratio of the real power flowing to the load over the apparent power =
in
>> =A0 the circuit,[1][2] and is a dimensionless number between 0 and 1
>> =A0 (frequently expressed as a percentage, e.g. 0.5 pf =3D 50% pf).
>> =A0 [...]
>> =A0 Circuits containing purely resistive [loads] have a power factor of
>> =A0 1.0. Circuits containing inductive or capacitive elements (electric
>> =A0 motors, solenoid valves, lamp ballasts, and others ) often have a
>> =A0 power factor below 1.0.
>>
>> So when PF=3D1.0, VA=3D=3DWatts. The better the quality of your power su=
pply,
>> the closer its PF will be to 1.0. In the last decade it has become
>> common for name brand computer power supplies to specify a PF as a
>> selling point.
>>
>> See also:
>> http://en.wikipedia.org/wiki/Switching_regulator#Power_factor
>>
>> for discussion of PF with respect to computer power supplies.
>>
>>
>>> When you're talking about 208, you're talking 3-phase.
>>
>> You can attach single phase loads to a multi-phase supply, as long as
>> they are balanced:
>> http://en.wikipedia.org/wiki/Three-phase_electric_power#Single-phase_loa=
ds
>>
>>
>>> If you want to use 3-phase 208, you need a special power supply in the
>>> server. =A0Generally you don't have such a thing...
>>
>> Old power supplies used to have a 120V/240V mechanical switch. Most
>> modern switching supplies will work fine with any input voltage from
>> like 90V up to 250V (check your supply specifications). The ability to
>> handle a wide input range is a byproduct of the switching regulator
>> design:
>>
>> http://en.wikipedia.org/wiki/Switching_regulator
>>
>> =A0-Tom
>>
>
>
> --
> Jerry Feldman<gaf at blu.org>
> Boston Linux and Unix
> PGP key id:3BC1EB90
> PGP Key fingerprint: 49E2 C52A FC5A A31F 8D66 =A0C0AF 7CEA 30FC 3BC1 EB90
>
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