Stackable Switches - why is it better?

[dgsmith]

When we redesign our infastructure during the summer, one of the things I am inclined to include is a stack of "stackable" switches (3x 48port), as opposed to the current setup of a single copper link between them. Does having stackable features differ significantly, and are they worth the extra money? I know they are easily managed by single IP in the management interface, but what else is desirable?

 

For instance, the Netgear stackable (using GS748TS as an example) has HDMI connections at the rear which I believe can provide around 20gbps throughput between switches, which of course is significantly more than single copper links.

 

On the other hand, I have been looking into some HP switches to do the same job (on a budget), so noticed the Procurve 2810 series include "virtual" stack ability within them. How does a physical stack with the NG compare with the "virtual" stack as described in the HPs? Can the high throughput between switches be achieved on the HP as well as the NG? If anyone has this model of HP switch or knows of them, how does the stack work (ie: just copper links or is there special connectivity).

 

Cheers,

Dave

[Geoff]

Stackable switches IMHO are only worth it when you have devices connected to the stack talking to each other a lot (for example, a data centre). Now I don't know how your network topology is laid out but at my school, the servers are no where near where the IT suites are. Everything in the suite has to talk to the servers down the same bit of fibre and hardly ever to each other. Thus using stackables doesn't make much sense.

[localzuk]

We make use of a virtual stack with our 2600 series switches. The functionality isn't there to improve bandwidth but to reduce configuration hassle - some configuration options simply get copied over to the members of the stack.

 

And as Geoff says, I don't get stacks for edge units - the bottleneck is the link to the core. We make use of a fibre connection to each edge switch in our school, and where there wasn't capacity, I pushed for, and got, new fibres installed.

[dgsmith]

What we're looking at is a core switch (either GSM7212 if we go netgear, or HP 2810-24G if we go HP), with 3x 48port switches below this in the same cabinet, serving the new ICT rooms we are getting (within close proximity). I like the idea of stacking for configuration and ease of management purposes (especially when multiple switches are involved, with the future likelyhood of expansion), though my uncertainty before lied with the issue of bandwidth on and among the stack.

 

I suppose it might be sufficient enough to have maybe 2 copper links from each stacked switch back up the core, thus providing each 48port stacked switch with 2Gbps bandwidth from the core? (fibre to EACH switch I don't see a need for, given all are in the same cabinet to the core).

On the other hand, if these were stacked, would it mean only 1 switch would need to have this link from the core (to save on ports for use with clients), or would bandwidth be noticeably affected?

 

As we have never really had or dealt with any decent switches (and only a few smart managed have been fitted recently), stacked switches in particular is an area I know barely much about, so knowing what the benefits are may help in decision making!

[Michael]

Taken from the HP 2810 manual:

 

The Series 2810 Switch devices can be connected together, through standard network connections, and managed through a single IP address. Up to 16 switches can be connected together in such a “virtual stack”. You identify the switch as the “Commander” and give that switch an IP address.

Up to 15 other switches in the network can then easily be configured as Members of the stack and managed through the Commander’s IP address. The management includes Telnet access and web browser interface access to the Commander and to each Member switch through the Commander.

 

I can highly recommend HP switches. I've never installed a HP 2810, however I have recently installed a HP 2626-PWR and it is superb. As a word of caution, I would check the depth of these switches. They all conform to a standard 19" cabinet, but the bigger and better switches are, the deeper they are!

 

You're also absolutely right about using CAT5e or CAT6 to connect the switches together. Fibre is not necessary as switches are in close proximity. Hope this helps.

[sidewinder]

I dont use stacked switches a lot anymore, most of ours are now Procurves which dont have the capability anyway (aside from the virtual option mentioned above) The few areas I do it is purely because there isnt enough capacity at the core to provide fibre to each switch individually, but this should be resolved later in the year.

There is a management benefit having a stack, in that you only need 1 IP and only need to configure things once, but not any performance benefit IMO

[torledo]

The 'virtual' aspect with most stackable switches is the idea of managing the entire stack from a single ip address or single mangement pane......therefore they're designed to aid manageability.

Another advantage related to this is fault tolerance through the use of dual paths between switches.

 

Hence the idea of a virtual chassis. In the case of a stackable solution the backplane between switches is the cabled interconect which ofcourse differs from a chassis based solution. Another difference compared to a chassis is that you have to supply redundant power to each switch.

 

There's absolutely no reason whatsoever why you can't use them in the edge - it really all depends on the physical layout of you're network. If you've got a cabinet that concentrates 100+ horizontal network connections you can use a stack of 3 or more 48 port edge switches with x number of uplinks. This shouldn't be a bottleneck if you've got enough bandwidth through link aggregated uplink ports or even better 10gbps to the core. This all depends on the aggregate throughput going form the stack to the core.

 

Physically switch vendors implement a stack in different ways. HP use dual personality ports for use as the stack interconnect. Similar to how cisco do it with using the fiber ports on the 3560 range. The cisco 3750 uses a dedicated switch interconnect called stackwise. This is a unique connector and cable that connects to the back of each switch in a daisy chained fashion. Advantage of a dedicated interconnect is increased bandwidth (stackwise hits a whopping 32gbps) plus also means none of you're fiber ports are taken up by the stack interconnect.

[localzuk]

What we're looking at is a core switch (either GSM7212 if we go netgear, or HP 2810-24G if we go HP), with 3x 48port switches below this in the same cabinet, serving the new ICT rooms we are getting (within close proximity). I like the idea of stacking for configuration and ease of management purposes (especially when multiple switches are involved, with the future likelyhood of expansion), though my uncertainty before lied with the issue of bandwidth on and among the stack.

 

I'm confused. Are you looking to create a core or edge set up? So, you have your servers and edge switches connected to a switch (what I'd call, and most on here would call a core), and want a stack in a remote cabinet connecting back to that core? What is the 2810 unit for?

 

I suppose it might be sufficient enough to have maybe 2 copper links from each stacked switch back up the core, thus providing each 48port stacked switch with 2Gbps bandwidth from the core? (fibre to EACH switch I don't see a need for, given all are in the same cabinet to the core).

On the other hand, if these were stacked, would it mean only 1 switch would need to have this link from the core (to save on ports for use with clients), or would bandwidth be noticeably affected?

 

The more units you connect together to rely on a single backbone link (fibre or copper) the more of a bottleneck you create. This is why all our units connect back direct with each having a fibre. It creates a true star network with no individual switches being a bottleneck.

 

As we have never really had or dealt with any decent switches (and only a few smart managed have been fitted recently), stacked switches in particular is an area I know barely much about, so knowing what the benefits are may help in decision making!

 

A stack allows for higher speed communication between end nodes, but if those nodes don't often need to communicate with each other (which, in a normal school network they won't) then there isn't much point in a stack. Personally, I try to ensure at least 1GB bandwidth back to the core for each 48 end nodes.

[torledo]

What we're looking at is a core switch (either GSM7212 if we go netgear, or HP 2810-24G if we go HP), with 3x 48port switches below this in the same cabinet, serving the new ICT rooms we are getting (within close proximity). I like the idea of stacking for configuration and ease of management purposes (especially when multiple switches are involved, with the future likelyhood of expansion), though my uncertainty before lied with the issue of bandwidth on and among the stack.

 

I suppose it might be sufficient enough to have maybe 2 copper links from each stacked switch back up the core, thus providing each 48port stacked switch with 2Gbps bandwidth from the core? (fibre to EACH switch I don't see a need for, given all are in the same cabinet to the core).

On the other hand, if these were stacked, would it mean only 1 switch would need to have this link from the core (to save on ports for use with clients), or would bandwidth be noticeably affected?

 

As we have never really had or dealt with any decent switches (and only a few smart managed have been fitted recently), stacked switches in particular is an area I know barely much about, so knowing what the benefits are may help in decision making!

 

As i've mentioned, how much bandwidth you need to provide to the core depends on you're environment. Technially, as a stack is a single switch for mgmt purposes you only need connect ports from a single switch to the core - all member swtiches will use the ports on that switch to reach the core. Provide too few connections to the core and you get the potential of bottleneck - plus you've got a single point of failure with only connecting one switch to the core becuase each switch in the stack has independent power and electronics...but there isn't a hard and fast rule for how many links you should provide. Technically for a stack you don't need to connect each switch to the core.

 

@localzuk - it woudn't be a bottleneck if the link to the core was 10gbps

Edited March 9, 2008 by torledo

[FN-GM]

If you use 2 cables instead of one for stacking will this increase network speed?

[torledo]

If you use 2 cables instead of one for stacking will this increase network speed?

 

No, the second cable for switch stacking is usually for connecting to a second neighbouring switch. Or in the case of the last switch in the stack for connecting back to the first switch. Thus creating a complete stack, but not a fell mesh if there are more than three switches in the stack.

[dgsmith]

I'm confused. Are you looking to create a core or edge set up? So, you have your servers and edge switches connected to a switch (what I'd call, and most on here would call a core), and want a stack in a remote cabinet connecting back to that core? What is the 2810 unit for?

 

A core setup; looking at a 2810-24 for the actual core switch, then within the same cabinet, 3x 48port (2810-48 for example), so those 48porters could copper link into the core, possibly in aggregrated links.

 

The more units you connect together to rely on a single backbone link (fibre or copper) the more of a bottleneck you create. This is why all our units connect back direct with each having a fibre. It creates a true star network with no individual switches being a bottleneck.

 

Given the distance between the new core switch and these 48port stacked switches will be a few inches, for us, going fibre to each switch here would be rather pointless - though if the money is there and the capacity, sure, go for fibre to the edge switches, but our funding can't stretch to that

We have fibre to each cabinet around the school, which will just be that 1 fibre link connecting into the core (there will be 4 fibre links in total).

 

A stack allows for higher speed communication between end nodes, but if those nodes don't often need to communicate with each other (which, in a normal school network they won't) then there isn't much point in a stack. Personally, I try to ensure at least 1GB bandwidth back to the core for each 48 end nodes.

 

My main initial bandwidth concern was related to the switches in the stack which may not have been connected by copper to the core (dependant upon capacity), and literally getting bandwidth from switches higher up the stack. I guess, if we go for 2 aggregated links to each stacked switch to the core (so 6 core ports taken), then bandwidth should not be an issue; though, I am still liking the stack route for managemant/config reasons.

 

10Gb maybe in many years to come, but we couldn't possible explain why we need that just now!

Edited March 9, 2008 by dgsmith

[localzuk]

Ok, so personally I would go with something like a 2900-48G series at the core and a bunch of 2810-48's as the 'stack' with aggregated links back to the 2900-48G.

 

There isn't really any need for a full fledged stack IMO.

 

Or if you can't afford that, go down a level and have a 2810-48 as the core and 2650's as the lower ones. But this removes gigabit from the end nodes.

[Jobos]

Sorry to drag this thread from the grave but I’m confused… with reference to the core switch. Is the core switch a switch that is used solely to connect other switches together? i.e. work stations are not connected to this core switch?

[Geoff]

Correct. In theory you should end up with a 'star' shaped network topology. With each of your 'edge' switches running back to your 'core' switch. In larger sites you'll probably have multiple 'core' switches strung together to form your 'backbone' thus giving you multiple 'star' networks. Usually this is laid out to coincide with your physical buildings/sites/etc

[wesleyw]

Looking at this thread wouldn't it have been better to just have the core switch loaded with the extra Copper ports he'd have needed then the connection speed si the backplane speed anyway which is usually considerably higher than anything but several trunked 10gb fibre ports (I know Extreme, Cisco and Foundry are much faster than this)? Just seems a little strange to have a core switch and then add several switches below if you can get a core with enough upgrade capacity why not use it?

 

 

Wes

[flyinghaggis]

Looking at this thread wouldn't it have been better to just have the core switch loaded with the extra Copper ports he'd have needed then the connection speed si the backplane speed anyway which is usually considerably higher than anything but several trunked 10gb fibre ports (I know Extreme, Cisco and Foundry are much faster than this)? Just seems a little strange to have a core switch and then add several switches below if you can get a core with enough upgrade capacity why not use it?

 

 

Wes

 

Ideally I think you would do the above as long as the devices you're connecting all lead back to the same comms cabinet/patch panel location.

Most of the PCs in our school are in different buildings from where the core switch/cabinet is located with fibre links connecting them (between seperate buildings) hence the need for a core and several 'edge' switches. I'm sure a lot of other places will be in the same situation.

Many of the modular switches that take substantial numbers of fibre/ethernet connections are also fairly expensive so if funds are limited it might be cheaper to buy a stack of several lower cost switches.

Edited February 20, 2009 by flyinghaggis