Need help understanding Exchange 2007/2010 clustering

Would appriciate come help understanding creating redundancy using exchange 2007/2010. SCR vs CCR, Do I need a SAN? What about for really large networks that need lots of storage, like 20,000 users. Thanks.
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Glen KnightCommented:
Exchange 2010 doesn't use clustering, it has database availability groups which do not require a SAN.  A copy of a database is housed in each server.

Exchange 2007 is very different.

CCR again requires no shared storage and further details can be found here:

SCR was introduced with SP1, and further details can be found here:
Muzafar MominCommented:
AmitIT ArchitectCommented:
For better redundancy you need server, site and disk resilency. Which you can do it with Exchange 2007 CCR and Exchange 2010 DAG only. Check below article for more understanding
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johnw885Author Commented:

How does exchange 2010 sync the databases? Over the network? or do you have the network/san option? Would you use a second nic for the network traffic and how does the syncing offset server resources. Wouldn't this double them?
I think that CCR is superior to SCR because a node failure is hardly noticed by users since the second node immediately takes over. There might be few seconds of outage while Exchange service is failing over to the second node automatically.
SCR requires a manual intervention in case of the Exchange Server failure.
You will definitely need SAN for 20000 mailboxes to accommodate needed IOPS. In other words you will need more disk spindles than you can fit in a server. There is a good tool that can calculate the storage configuration for you (including the number of spindles you will need).:

As for general storage config, here is a MS article that has links to other articles that will help with deciding on the technology to use:

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johnw885Author Commented:
Thanks for the info
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