3750X stackpower testing

[devendrakarthik]

Hi,

I have 2 WS-C3750X-24T-S switches that I would like to use as a stack. Each has come with one 350WAC power supply. Does a single 350WAC powersupply support two switch stack. Meaning, if plug out powersupply of one switch, will the stack be still running? There is absolutely no load on the stack as this is purely for testing purpose.

If not, let me know if there is any other way...like installing both 350WAC on one switch and bringing up the other switch using stack power ( donno if this is really possible?). Though not the ideal production scenario but will help me in testing stackpower.

What is the minimum power a 3750X would require to be up?

Thank you...

Regards,

Karthik.

[Reza Sharifi]

Hi Karthik,

I tested this with 2 3750-X-24, but each with 715WAC Power supply.  When I unplug the power from one of the switches, the switch gets its power from the other switch and continue to operate normally.

I don't know if it works the same way with 350WAC power supply, but It should, if you don't have much of load on both devices.

HTH

Reza

[letsgomets]

Your scenario will work. Cisco does not recommend going beyond a stack of 4 switches for this technology.

To answer your final question

When the Cisco StackPower solution is configured in redundant mode, it aggregates all of the power available in the stack (from all power supplies in the stack) and then subtracts an amount of power that it keeps in reserve. The amount of reserved power is determined by the size of the largest power supply in the stack. The remaining power is used to power up all of the switches and PoE devices similar.

This mechanism allows the stack to be resilient and withstand a single power supply failure, regardless of the type of power supply that fails. That is, the failed power supply could be 350W, 715W, 440W DC, or 1100W, and the system can protect against that failure because the "reserved" power is sized for the worse case.

Notice that no mechanism allows the stack to be resilient and withstand a single power supply failure, regardless of the type of power supply that fails. That is, the failed power supply could be 350W, 715W, 440W DC, or 1100W, and the system can protect against power supply is singled out or placed in reserved mode. All power supplies are online, and the StackPower solution works with the overall budget.

[devendrakarthik]

Thanks both for the replies

I have posed the same question to a Cisco expert during a webex session and below is what I have got:

­"Each switch takes 246W minimum power and hence you would require atleast 2 350W power supplies, or you can use 1x750W power supply­‑"

However, I could not find support data anywhere in the product literature.

Assuming first scenario fails(350WAC in each switch):

Do you think second scenario will work to boot up switch 2 that has no power supply with the help of switch 1 that has 2 x 350WAC now. I am referring to following FAQ from product literature.

Q. Can the Cisco StackPower solution boot up a switch that does not have a power supply?
A. Yes. By using the extra power capacity available in the stack, StackPower allows the system to supply power to a switch that does not have a power supply or that has a failed power supply

Note: My whole point is to determine the minimum power reqd when a switch(no PoE) is at max load and recommend the safest combination of power supplies for a 2 switch stack in production environment.

Regards,

Karthik.

[hobbe]

To answer your new question.

the safest you can do for a 2x24port non PoE solution would in my eyes be having 4 715w/1100w connected to 4 different powersources.

Ie 2 via ups and 2 via 2 different power stations.

however that might be a bit overkill.

2 715 w would do the trick just nicely. one to power them and one spare

There are several reasons why one would like to have 2-3 powersupplys.

if you have 3 then you can switch power outlets by alternating and still keep your SLA.

for 4 switches in a stack you can use 2 or 3 1100  and do just nicely.

good luck

HTH

[hobbe]

Hi

I have tested just that, and it works.

I have 2 3750x with 2 350 and 2 715 powersupplys.

I have run both the switches of one 350w powersupply.

it should not work but it does. it might be that the powersupply itself uses alot of energy, or that the processor and motherboard is just ideling.

you can test it through shutting down powersupplys through the cli commands

actually its kind of wierd but you can actually shut down the last remaining powersupply also causing the switch stack to reload.

There are actually many different things you can do to change the powerconsumption of a stack.

you can shutdown ports and choose what switches to shutdown incase of powerfaliure.

it realy rocks !

HTH