Exchange 2007 - SCC/CCR and SCR

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ermmau Posted: 12-19-2007 9:13 AM

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Hello,

 In a SAN environment, what is better to choose to allow availability and resilience with EX2007 .... is CCR better that SCC or there are specific issues to choose one instead of the other?

Is it possible to have a mixed architecture environment where X64 main site uses a X86 backup site replicated with SCR?

 Regards

-ermmau

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Joel Stidley replied on 12-19-2007 10:42 AM

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The new recommended configuration is CCR.

Why you might ask? Even though CCR doesn't require SAN attached disk however it provides two copies of the data for redundancy in case of drive failure. This allows for larger databases and quicker restore times because two copies of the data are on disk at all times. Some advanced SAN backup features are also available.

You can't use an x86 server as an SCR target because it requires Exchange Server 2007 SP1 to be installed which is only supported in production on x64 editions of Windows Server.

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ermmau replied on 12-20-2007 1:57 AM

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I'm asking because of having SAN and using CCR means doubling the space in an environment that already has a good redudancy of the data.

With SAN using consistent snapshots you could have the same speed in restore of double copy using opimized space usage. CCR with one SAN, seems to be a non-sense redudancy if you don't have a duplicated SAN that is it doesn't resolve the SPF on the SAN and doesn't increase the overall speed ... If you consider that the replication between the two Information Stores goes through the servers ... this could result in slowing the performance because of the three steps you need to copy from one IS to the second on the SAN.

Also what about virtualization support on VMWARE. Is this solution supported (I know it is working) in the SCR environment?

Thanks

- ermmau

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Joel Stidley replied on 12-20-2007 11:50 AM

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First of all I agree with you, it seems a bit much to have to allocate double the space for CCR and is a difficult sell to most customers. One way that Microsoft tries to reason this out is that you don't really need a SAN to use CCR, you can use DAS and reduce your cost. Of course, you will sacrifice the ability to use VSS hardware-base snapshots. 

You are also right that if you have both servers connected to the same SAN or storage controllers you have a single point of failure, however it is hopeful that there is at least some redundancy built in to that SAN. Ideally, seperate SANs or storage controllers would be used, however this seems unlikely in most shops.

Now you made a couple other good points but I think they can also be reasoned the other way as well:

1. "Using consistent snapshots you could have the same speed in restore of double copy using opimized space usage"
• This isn't entirely true as a CCR failover can happen in just a few seconds, and a VSS restore would require a full outage and some jockeying to complete in the event of a disk/lun failure on the active node.
2. "CCR means doubling the space in an environment that already has a good redudancy of the data"
• If you are using VSS snapshots you are also using double the disk, using CCR may reduce the number of VSS snapshots that you need to keep since you always have an active second copy on disk. Although you are probably using RAID 0 for the snapshots, the space difference may not be as steep as you think.

As for VMWare ESX/Server, Microsoft does not provide support for Exchange Server 2007 in any virtualize environment (at least until Hyper-V is available), you will have to obtain primary support through VMWare or will have to reproduce the problem on a physical server for Microsoft support.