High level Exchange 2010 architecture

Here are some questions I had from a college in Ohio wanting to plan for Exchange Server 2010:


What does the Exchange 2010 architecture look like?


The 5 Exchange 2010 roles are the same but there are some major changes in the way things work:

Outlook 2007+ MAPI clients now connect through CAS rather than directly to the mail server. CAS also provides access to directories for any Outlook needs.


Plan on scaling out CAS arrays with NLB or HWLB based on the core ratio below.


Hub transport now has a shadow redundancy feature and new dumpster changes.


The shadow redundancy feature would be where a shadow copy of each sent email is retained on the hub and until the hub received a ack of successful delivery. In the example above if Edge1 has a failure after the message has left the hub, the hub would not receive a discard ack and after 3 retries (15 min) the hub transport would then resend the shadow copy of the message to Edge2. It can also work with some downstream MTAs (Exchange, SMTP, etc) where the hub transport can wait for a specified interval for an Ack and resubmit.


The hub also has a new dumpster feature where the hub communicates with the mailbox server around replication and availability status. This communication determines whether or not to purge older messages in the dumpster until all logs have been replicated and communication has been re-established.


What are the beta HW recommendations for ballpark HW estimation? (note: this is with beta and subject to change) :

Client Access Server (CAS)

CAS to Mailbox ratio = 3 : 4 processor cores

8 cores recommended, 2GB RAM per core

Hub Transport server

Hub to Mailbox ratio : 1 : 7 (no A/V on Hub) or 1 : 5 (with A/V Hub) processor cores

4 cores recommended, 1GB RAM per core



4-8 cores, 4GB RAM base + 2-8MB per mailbox based on mail profile


4 cores, 4-8GB RAM total

Edge guidance expected to be very similar to Exchange Server 2007

2 to 4 cores

Global catalog to Mailbox ratio 1 : 4 (32–bit GC) or 1 : 8 (64-bit GC) processor cores


What storage do I need?

Since the IOPS per user is proposed to be another estimated 70% reduction, this translates to several new storage options in Exchange Sever 2010 where you can use cheaper SATA direct attach storage or even JBOD SATA with DAG.  See our storage post here.

Comments (2)

  1. markga says:


    It depends on where your CAS servers are placed. If you have multiple CAS roles in the same AD site then it would not necessarily use the locally hosted CAS.  Your CAS array would be load balanced with NLB or HWLB. One note when combining roles, you cannot have NLB and DAG on the same server so you would have to leverage a 3rd party LB.

    ISA 2006 would direct all client traffic via HTTPS to the CAS roles via a NLB or HWLB VIP address.

    Thus far the beta recommendations are 8 core for CAS and 8 core for multi role  (16 max) – The final HW and proc core recommendations will be coming after RTM of Exchange 2010.



  2. Brian says:

    In Exchange 2007 the HUB roll on a mailbox server would see only that HUB being used by clients on the MB server. With all rolls being supported on a each box (even if it’s in a DAG) would the clients of one MB server only use that CAS (ala redirect to your CAS) or would they still all be split. How does this impact ISA publishing OWA if all your CAS are on each MB server. With IO requirements being lower and CAS doing all the client connections a single 16 core server with 32GB of RAM looks more attractive than 1 with 4 cores and 4G (HUB) 2 with 8 cores and 16GB (CAS).

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