Server farm design under 3 tier design

Question

Hi guys,
Just wondering which is best practise?
connect server farm into distribution switches or connect directly to core switches?
Understand from different articles stated different methology but from what i see in cisco network design, server farm is always connected to the distribution switches.
What other factors to consider when connecting to distribution and when to consider when connecting to core ?
Thanks

Answer 1

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Jon, very nice reply.  Thanks for joining this thread.
This makes sense because what real value would a dedicated core provide. If traffic is routing between vlans it does this on the distro switches and the only time it routes anywhere else is to the WAN and you do not high speed core switches to do this.
Yep, in in my cited example, the 4th 6509 uses its 6708's for two off-site 10g links.
I have also done the same as Joseph and connected servers to a collapsed pair of distro/core switches primarily because of cost but also because your core/distro switches tend to have the greater throughput so it is a logical place to put them.. In addition because they are on the core/distro switches you do not have to worry about oversubscribing uplinks from a different pair of switches, although there might still be oversubscription on the core/distro switches.
Re: cost, again, yep, why buy another box?
Re: greater throughput, also again, yep, for example, note I noted 4th box is all CEF720, i.e. all fabric, vs. classic bus in user 6509s.
Re: oversubscription, and again, yep, 4th 6509's server 6748 cards are 40 Gbps to fabric, vs. gig or even 10g uplinks from a separate server switch.
Jon, one reason I enjoyed, so much, reading you've done similar for similar reasons, late last year the business unit came to me and told me they want a separate dual core to increase reliability (as call centers are considered critical).  I noted that, yes, adding a second "core" box, by adding a redundant chassis (vs. the single chassis with redundant everything else) would decrease the MTBF by about 2 hours a year for the off-site links (expensively, IMO, for those 2 hours, but as they are footing the bill, who am I to say no), but I didn't see any advantage for adding another (2nd) "core" box (vs. continuing using the existing box as a collapsed core).  Well I got overruled because you just can't share a "core" device for anything else .
Unfortunately, a case of, I think, some reading some design guides, which say "core" devices do X, and so therefore, you can never do otherwise.  Again, so very much enjoyed reading someone else not following the 3 tier model, always, literally.