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New Member

MPS or Backplane for Switch selection

Folks,

I have a design question here.

When I select a switch for a server farm, what shall I consider as switch capacity. Million packet per second or backplane capacity of the switch?

This situation comes when I need to select a switch for a rack where multiple servers resides.

The same question arises in case routers also.

2 ACCEPTED SOLUTIONS

Accepted Solutions
Super Bronze

Re: MPS or Backplane for Switch selection

Disclaimer

The   Author of this posting offers the information contained within this   posting without consideration and with the reader's understanding that   there's no implied or expressed suitability or fitness for any purpose.   Information provided is for informational purposes only and should not   be construed as rendering professional advice of any kind. Usage of  this  posting's information is solely at reader's own risk.

Liability Disclaimer

In   no event shall Author be liable for any damages whatsoever (including,   without limitation, damages for loss of use, data or profit) arising  out  of the use or inability to use the posting's information even if  Author  has been advised of the possibility of such damage.

Posting

To answer that question, you need to know just how busy your servers are going to be and what their traffic characteristics will be.

One "easy" answer is to compute capacity assuming minimum size Ethernet packets, and all ports running at 100%.  For 8 Gbps (duplex) you would want a switch that has a non-blocking fabric that provides 16 Gbps (twice the port bandwidths) backplane capacity and 11.9 Mpps (1.488 Mpps per Gbps).

Real world (especially edge) switches rarely run this kind of load, but if the switch supports it, you're guaranteed wire-speed or line-rate.  (Many "modern" Enterprise grade switches support wire-speed/line-rate.)

As I mentioned in my initial post, besides bandwidth and PPS, there's buffering resources to consider.  In real world networks more than one device may transmit to the same device or one device might have a higher bandwidth connection.  Then it's not a just a question of raw performance, but how much of a data the switch might be able to buffer.

Just "knowing" 8 servers with gig NICs isn't enough information to select the "best fit" switch.

Super Bronze

Re: MPS or Backplane for Switch selection

Disclaimer

The   Author of this posting offers the information contained within this   posting without consideration and with the reader's understanding that   there's no implied or expressed suitability or fitness for any purpose.   Information provided is for informational purposes only and should not   be construed as rendering professional advice of any kind. Usage of  this  posting's information is solely at reader's own risk.

Liability Disclaimer

In   no event shall Author be liable for any damages whatsoever (including,   without limitation, damages for loss of use, data or profit) arising  out  of the use or inability to use the posting's information even if  Author  has been advised of the possibility of such damage.

Posting

ok..so if the device manufacturer doesn't provide the information and it is also not in the datasheet, then it is a compromising situation right? We have to assume then or have play safe.

Yep.

BTW, the manufacturer's recommended role for the switch sometimes help.  Switches designed for user edges usually have less hardware resources than those recommended for server edges than those recommended for distribution/core.  On chassis switches, similar might apply for different line cards.

Also what sometimes help is 3rd party review of one switch vs. another.  I.e. search the Internet for switches of interest.

7 REPLIES
Super Bronze

Re: MPS or Backplane for Switch selection

Disclaimer

The  Author of this posting offers the information contained within this  posting without consideration and with the reader's understanding that  there's no implied or expressed suitability or fitness for any purpose.  Information provided is for informational purposes only and should not  be construed as rendering professional advice of any kind. Usage of this  posting's information is solely at reader's own risk.

Liability Disclaimer

In  no event shall Author be liable for any damages whatsoever (including,  without limitation, damages for loss of use, data or profit) arising out  of the use or inability to use the posting's information even if Author  has been advised of the possibility of such damage.

Posting

You need to account for both.

PPS can be "tricky" as its varies based on packet's size.

You also may want to account for buffer resources.

New Member

MPS or Backplane for Switch selection

Hi Joseph,

if the servers have gigabit ethernet card and say 8 servers are connecting to a switch on top of the rack, then how we will calculate and select the switch?

Assume total port required is 24. My intention is to know how select the right switch which will not create capacity constraint.

Super Bronze

Re: MPS or Backplane for Switch selection

Disclaimer

The   Author of this posting offers the information contained within this   posting without consideration and with the reader's understanding that   there's no implied or expressed suitability or fitness for any purpose.   Information provided is for informational purposes only and should not   be construed as rendering professional advice of any kind. Usage of  this  posting's information is solely at reader's own risk.

Liability Disclaimer

In   no event shall Author be liable for any damages whatsoever (including,   without limitation, damages for loss of use, data or profit) arising  out  of the use or inability to use the posting's information even if  Author  has been advised of the possibility of such damage.

Posting

To answer that question, you need to know just how busy your servers are going to be and what their traffic characteristics will be.

One "easy" answer is to compute capacity assuming minimum size Ethernet packets, and all ports running at 100%.  For 8 Gbps (duplex) you would want a switch that has a non-blocking fabric that provides 16 Gbps (twice the port bandwidths) backplane capacity and 11.9 Mpps (1.488 Mpps per Gbps).

Real world (especially edge) switches rarely run this kind of load, but if the switch supports it, you're guaranteed wire-speed or line-rate.  (Many "modern" Enterprise grade switches support wire-speed/line-rate.)

As I mentioned in my initial post, besides bandwidth and PPS, there's buffering resources to consider.  In real world networks more than one device may transmit to the same device or one device might have a higher bandwidth connection.  Then it's not a just a question of raw performance, but how much of a data the switch might be able to buffer.

Just "knowing" 8 servers with gig NICs isn't enough information to select the "best fit" switch.

New Member

MPS or Backplane for Switch selection

Hi Joseph,

I understand what you are saying. I want to know where are the resources where I will be able to get the information of switch and router capacity. I think buffer means the ques in the ingress and egress port of the switch you mean? So can I consider that we have 3 major factor to consider here. 1. PPS 2. Backplane and 3. Buffering capacity (includes how fast the switch clears the buffer?)

Super Bronze

Re: MPS or Backplane for Switch selection

Disclaimer

The  Author of this posting offers the information contained within this  posting without consideration and with the reader's understanding that  there's no implied or expressed suitability or fitness for any purpose.  Information provided is for informational purposes only and should not  be construed as rendering professional advice of any kind. Usage of this  posting's information is solely at reader's own risk.

Liability Disclaimer

In  no event shall Author be liable for any damages whatsoever (including,  without limitation, damages for loss of use, data or profit) arising out  of the use or inability to use the posting's information even if Author  has been advised of the possibility of such damage.

Posting

Ideally performance specifications are listed on device's data sheets.  If not, you may need "dig" through other documentation and/or contact the device's manufacturer, who may, or may not, provide it.

New Member

MPS or Backplane for Switch selection

ok..so if the device manufacturer doesn't provide the information and it is also not in the datasheet, then it is a compromising situation right? We have to assume then or have play safe.

Super Bronze

Re: MPS or Backplane for Switch selection

Disclaimer

The   Author of this posting offers the information contained within this   posting without consideration and with the reader's understanding that   there's no implied or expressed suitability or fitness for any purpose.   Information provided is for informational purposes only and should not   be construed as rendering professional advice of any kind. Usage of  this  posting's information is solely at reader's own risk.

Liability Disclaimer

In   no event shall Author be liable for any damages whatsoever (including,   without limitation, damages for loss of use, data or profit) arising  out  of the use or inability to use the posting's information even if  Author  has been advised of the possibility of such damage.

Posting

ok..so if the device manufacturer doesn't provide the information and it is also not in the datasheet, then it is a compromising situation right? We have to assume then or have play safe.

Yep.

BTW, the manufacturer's recommended role for the switch sometimes help.  Switches designed for user edges usually have less hardware resources than those recommended for server edges than those recommended for distribution/core.  On chassis switches, similar might apply for different line cards.

Also what sometimes help is 3rd party review of one switch vs. another.  I.e. search the Internet for switches of interest.

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