Exchange 2007 SCC or CCR?

Hello all-

I am designing an enterprise deployment for a client with around 20000 mailboxes.  My initial design had x5 2-node CCR clusters serving the mailboxes.  The client currently has x2 6 node clusters (2k3) and would like to know why we cant keep that model. (would be an SCC model with 2k7)  Our SAN is a brand new EMC CX-4, so the single point of failure at the database seems like a relatively low risk.  Is there any other reason for me to keep pushing CCR?  I'm relatively ambivalent towards either option-

Thanks!
PallidaMorsAsked:
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Malli BoppeCommented:
CCR is a better option compareded to SCC.With CCR you have 2 copies of databases and with SCC just one copy.
http://msmvps.com/blogs/clusterhelp/archive/2007/10/31/which-exchange-server-2007-server-cluster-type-should-i-use-ccr-or-scc.aspx 
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Matthew EnglandTechnology ConsultantCommented:
I would stick with to your design. With very few exceptions I find that more than two Exchange nodes is usually excessive. The two node CCR design will provide your client with a solid system, with the 24x7 capabilities they're obviously looking for although, should an incident occur when a node is offline for maintenance.

It sounds like your clients concerns are viable. After spending money on the SAN storage, CCR may seem both like a waste of that space & if the second copy's of the database are going to reside on the same SAN, a bit silly to them. Find out how your disk groups in the SAN are configured, specifically how many physical disks you could lose before data loss occurs. You may be able to appeal to them pointing out that with CCR you can have a copy of the Exchange stores on a different set of disks, increasing the fault tolerance on the back end, where it really matters, and you would be able to do so while actually improving system performance since backups could be performed on the passive Exchange instance with CCR. (A benefit you don't have with SCC, since increasing disk redundancy on the SAN means reducing I/O performance, and/or shrinking your available storage pool.)

It also sounds as though your client has a centralized datacenter. If they have, or plan to have a continuity of operations site, you can also use that to help persuade them that CCR is a good option. Since CCR can span data centers this would be a practical and much faster method of bringing up Exchange at the remote site in the event of a site related issue. Even if they're not interested in this benefit now, convincing them to establish the CCR cluster, will provide them the flexibility to implement this type of option down the road with minimal re-configurations.

The hurdles, as it seems, will be disk space cost, and convincing the client that two instances of the data store is better than one. The other would be getting them to give up a bit of front end redundancy. You may want to probe them for some history. Have they had major outages or stability issues in the past that lead to their feelings that six nodes are necessary?

Ultimately it's your clients decision. If you've provided them with the pro's and cons of both, provided information on industry trends and have given them your recommendations for what makes sense for their organization & their "IT roadmap", so to speak, then as you indicated, either option should provide them with a good degree of reliability.

The section, Selecting the Appropriate Availability Solution, in the following document may be of some help, assuming you haven't already read it:
http://technet.microsoft.com/en-us/library/bb123523(EXCHG.80).aspx

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PallidaMorsAuthor Commented:
Thanks for your help guys-  and great links, PacMIST...
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