[Dovecot] Multiple locations, 2 servers - planning questions...

[Charles Marcus]

On 2012-02-29 9:15 PM, Stan Hoeppner <stan at hardwarefreak.com> wrote:
> Q:  How many concurrent IMAP clients could you serve with this setup
>      before hitting a bottleneck at any point in the architecture?

No idea how to calculate it...

> What is the first bottleneck you'd run into?

Unless this is a trick question, the OC-12 link (since it is only 
644Mb), and the next bottleneck would be the 2 GbE server connections to 
the router (are these bonded? if so, what mode?...

> The correct answer to this question, and the subsequent discussion that
> will surely take place, may open your eyes a bit, and prompt you to
> rethink some of your assumptions that went into the architectural
> decisions you've presented here.

Since the vast majority of our connections will be *local*, I'm 
unconcerned about the internet connect speeds (one office has a 100/10Mb 
Cable (Comcast Business Class) connection, the other will have a 
100/100Mb fiber/ethernet connection).

My main priority is that the user experience at each physical location 
be optimal, which is why I'm more focused on making sure each offices 
users are connected to only the local server for all services 
(file/print/mail).

I also neglected to mention how each server would be physically 
connected to the network, which I guess I should have done, since I'm 
fairly sure that will be the bottleneck I should mostly be concerned 
about...

My choices are, as I see it, single GbE connections, or add some 
multiport GbE cards (these Dells support up to 3 PCIe cards) and bond 
some ports together for each VM. 10GbE is simply not in our price range 
(and I don't think we need it anyway), although I did stumble on these 
while googling and am waiting on pricing, since they claim to be 'much 
cheaper':

http://www.mellanox.com/ethernet/

Since neither the multi-port GbE cards or decent switches that have 
reliable support for bonding/teaming are really not that expensive 
(especially when comparing to 10GbE solutions), I don't really see any 
reason *not* to do this (at a minimum I'd get redundancy if one of the 
ports on the server failed), but I'm also not sure which mode would be 
best - round-robin or IEEE 802.3ad dynamic link aggregation?

Obviously, I don't have the experience or expertise to answer these 
questions myself (never analyzed IMAP traffic to have an idea of the 
bandwidth each user uses, and probably wouldn't trust my efforts if I 
made the attempt). Hopefully, there are some people here who have a 
rough idea, which is why I brought this question up here.

Oh - and I am/will be working with a local I.T. services company to help 
with the design and implementation (since obviously I don't have the 
experience to do this myself), and will be asking them these same 
questions, I just like to usually know the general answers to questions 
like this ahead of time, so that I know if the guys I'm hiring know what 
they are doing and are giving me the best options for my budget.

Thanks for your thoughts...

-- 

Best regards,

Charles