C9300 Stack query

[markh11]

I need to build several C9300 switches in stacks of 4.

I know how to connect the data and power stack cables, but want to know the answer to the following question.

Each switch has 2x power supplies. If all switches are powered up by these power supplies do I still need to use the power stacking cables?

Or can I just stack them with the data cables?

[balaji.bandi]

Depends on the requirement, as you mentioned if all switches are dual supply then Power stack cable not really required technically.

But Looking cost point of view. you save lot of Money when you do different combination.

Take example :

Switch 1 and 2 have 1100 Dual power supply

Switch 3 and 4 have only single 1100 Power supply

and you have dual feed coming to power on the switches, then if the Switch 3 and 4 power source off, you can easily get power from Switch 1 and 2, if thi.

If this is large deployment you save lot of cost and power too.

Pros and cons more information can be find here :

https://www.cisco.com/c/en/us/products/collateral/switches/catalyst-9300-series-switches/white-paper-c11-741945.html

[Joseph W. Doherty · Accepted solution]

Or can I just stack them with the data cables?

Usually, yes.

However, it actually depends on the power needs of each switch and its installed PSs.  But it's uncommon that two PSs cannot provide all the power needs of an individual switch.

As I understand it, the primary goal of stack power was to allow the failure of any one PS, in a power stack, without the need to lose the stack member or shed ports.

@balaji.bandi raises the attractive option of avoiding the need of meeting the power needs of individual stack members by sharing power between stack members.

On at least some earlier gen power stackable switches, there was (not well published) an amperage limit on the power stack cables.  I don't know if a similar limit still applies on the 9300 series.  But if there is, in the past, for example, you couldn't simply install a pair of the largest PSs in one stack power member and power all the other members from it (like a chassis).  However, on a stack of four, one PS installed in units 1 and 3 might support units 2 and 4 by wider distribution of amperage across the stack power cables.

@balaji.bandi correctly notes you cut expenses if you can reduce the number of PSs.  You might also reduce electrical usage too.

[julian.bendix]

If every switch has 2 power supplies, I usually don't go for the stack power cable and just skip those.

[Joseph W. Doherty]

If every switch has 2 power supplies, I usually don't go for the stack power cable and just skip those.

Actually, I've never been in an environment where we've used stack power cables.  (Often stacks would have more than 4 members, too.)

The power management features are impressive, but so was operational management using them, effectively.

The usual setup was dual like PSs, same wattage, either (usually) able to power that switch alone.  What our primary concern was, each PS, in the switch, was on a separate electrical source/branch.  I.e., if either electrical source/branch failed, stack stayed up.

So again, must you use the stack power cables, usually no.  Even when you do not need them, should you use them?  That's something you need to decide.

Also again, in earlier the stack power switches, amperage limits made using them, more complex.  But, don't know it that's also true for the C9300 series.

[MHM Cisco World]

If one SW use many UPoE and it power supply not enough' then sure he need power stack.

There is cisco tool to calculate the power needed

MHM

[Joseph W. Doherty]

---

@MHM Cisco World wrote:

If one SW use many UPoE and it power supply not enough' then sure he need power stack.

Yup, IF your total power need exceeds what two 1100W PSs can provide.  Which is unusual, but not impossible, as 48 UPOE ports all pulling their full 60W would total 2,880W.  Not many PoE devices are that power hungry, although APs . . .

Anyway, skimming the document reference @balaji.bandi provided, I find the power cables are limited to 55A.  So, 2,880W less 2200W (dual 1100W) less 110W (dual stack power cables), results in still being shy 570W, and I haven't even considered the power for the switch, itself.

Because of the power cable amperage limitation, I presume, @balaji.bandi's document does discuss taking care not to exceed the 55A limit, per cable.  For example, suggesting, in best practices, fill all the A PS slots before filling any of the B PS slots.

As I wrote in an earlier reply, it's the power management options impressive, as are operational usage considerations, too.

[MHM Cisco World]

Just to clear to him point need to cal his powers requirements 

MHM

[julian.bendix]

100% agreeing with you Joseph!

[markh11]

Thanks to everyone for all your answers