I had the privilege of attending Microsoft TechEd North America 2010 last week in New Orleans, LA and wanted to share a few confirmed new features of Exchange 2010 SP1 (due out later this year but no firm ETA).  The overall theme of this year’s TechEd was centered around, not surprisingly, cloud computing.  Specifically, Microsoft emphasized their mature Exchange Online offering but also stressed the growth of Windows Azure (Microsoft’s hosted services platform) and hosted SQL services.  The demonstrations of what Windows Azure and hosted SQL could do were extremely interesting and solidified Microsoft’s vision of being “all in” (according to keynote speaker Bob Muglia) with cloud computing.

Regarding Exchange 2010 SP1, a few of the Exchange sessions I attended had specific focus on SP1 and most of the others mentioned how different aspects of Exchange would change with SP1.  I discuss a number of my favorite changes/additions associated with SP1 below but please note that there are many more new features.  Please refer to the MS Exchange Team blog post on SP1 for more information.

Continuous Replication Block Mode

Continuous Replication Block Mode (CRBM) is, in my opinion, the most interesting and compelling new feature of Exchange 2010 SP1.  It is so important that it required a rename of the legacy continuous replication of Exchange 2007/2010 RTM to Continuous Replication File Mode (CRFM).  Basically, in CRFM or legacy continuous replication, the unit of replication in Exchange is a single log file.  Thus, after each 1 MB log file was closed on the active server (Exchange 2007) or database copy (Exchange 2010), the passive server or database copies would pull that log file and replay into the passive copy of the database.  This resulted in a worst case recovery point objective (RPO) of 1 MB (the active log stream) when replication was healthy and up-to-date.

CRBM is a dynamic continuous replication mode that is automatically turned on or off by Exchange 2010 when it detects that replication is completely up-to-date.  When turned on, CRBM allows Exchange to ship transactions committed to the active log stream to passive database copies.  Thus, the passive copies maintain their own log stream and can significantly reduce the RPO of Exchange in the event of a failure of the active copy.  However, while CRBM could bring your RPO down to individual transactions, I wouldn’t recommend advertising an RPO of less than 1 MB to a business owner since you cannot control CRBM and it may be turned off at any time.  In my opinion, it is better to advertise 1 MB and indicate that, under healthy replication circumstances, the realized RPO will likely be much better.

CRBM is not synchronous, so Exchange will not wait for an acknowledgement from the passive database copy that the log stream write succeeded.  Additionally, since a CRBM passive database copy now maintains its own log stream, it will automatically convert a partial log stream (log fragment) into a full log file for replay in the event of a failure of the active database copy.

Other High Availability and Site Resiliency Improvements

In addition to CRBM, SP1 will bring a number of other high availability and site resiliency improvements.  First, Outlook cross-site connection behavior will be more flexible by providing the option to have, in the event of a cross-site database failover, either a direct CAS connection from the CAS Array in the primary data center to the hosting Mailbox server in the secondary data center (default in RTM) or to disable this functionality entirely.  Second, Datacenter Activation Coordination (DAC) mode now becomes available for DAGs of all types, not just those with three or more members that are stretched across two or more sites.  Finally, improvements in gracefully shutting down log writes when a database activation is initiated removes the need for Exchange to perform a recovery process when a passive copy is activated.  This can reduce a typical database activation process from 30 seconds to 15 seconds.

Scott Schnoll at Microsoft has written a great article about these and other high availability and site resiliency changes in SP1 here.

Archiving and Discovery Improvements

As alluded to by Microsoft around when Exchange 2010 RTM was announced, SP1 will allow additional deployment flexibility with the Personal Archive.  First, formal support for Outlook 2007 will exist, although it will be limited to basic access to the Personal Archive.  Manipulation of retention policies and other aspects of the archive will be limited to Outlook 2010 and OWA 2010.  Second, SP1 will now allow storage of the Personal Archive in a different mailbox database than the primary mailbox.  Supported combinations of storage are primary and archive in the same mailbox database (on-premises or hosted), primary and archive in different mailbox databases (both on-premises), or primary on-premises and archive hosted.  While many law firms may find it difficult to adopt Exchange Online in the near term due to back-end application integration requirements with Exchange, the ability to host some users completely in the cloud and perhaps the Personal Archive for other users in the cloud as well is very intriguing.

Discovery becomes more robust by offering search preview to estimate anticipated discovery searches before executing a query, optional de-duplication of results in a completed discovery, and annotations for discovered content.

Outlook Web App Performance and Personalization Improvements

OWA performance has been improved dramatically in SP1 through a number of enhancements.  OWA will now pre-fetch content to make content presentation and reading faster.  Additionally, delete, mark as read, and categorization actions will now be asynchronous operations so that their results look instantaneous to the end user.  Long running operations, like large file transfers, will no longer be blocking operations that cause OWA hanging from an end user perspective.

OWA themes will make a comeback in SP1, with some prebuilt themes included and the ability to design your own (perhaps to match a corporate color scheme branding, etc.).  Furthermore, the administrator can granularly control if/how themes can be used.

Rich Coexistence with Exchange Online

Once Exchange Online is upgraded to Exchange 2010 SP1 later this year, coexistence between an on-premises solution and Exchange Online will become much more robust.  Due to the enhanced federated sharing features of Exchange 2010 (calendaring, etc.), traditional coexistence issues associated with free/busy lookups, internal mail classification, etc. are all resolved to provide much more seamless coexistence with Exchange Online.  With the ability to easily host and manage a subset of users in the cloud, this rich coexistence model makes this approach much more appealing.

As you can see, Exchange 2010 SP1 will provide many important new features to improve resiliency, flexibility, and performance of Exchange in a number of areas.  The SP1 Beta is available now, so check it out!

At a few recent client implementations, we have seen noticeable delays synchronizing various changes in mailboxes to Exchange 2010 when running Outlook 2003 in Online Mode.  As it turns out, this is a known issue and Microsoft has documented it at http://support.microsoft.com/kb/2009942.  The following are symptoms of the issue:

• Outgoing messages stay in the Outbox for up to 1 minute
• New messages do not arrive in the mailbox for up to 1 minute
• Items that are deleted or moved between folders may take up to 1 minute for the change to be reflected

This issue does not happen with Outlook 2003 in Cached Mode or in Outlook 2007/2010 in Online or Cached Mode.  The issue arises because Outlook 2003 requests UDP notifications from Exchange to determine when to retrieve messages.  When a new message arrives in an Exchange mailbox, Exchange 2007 and earlier would send a UDP notification to Outlook, which would then trigger Outlook to retrieve the message and display to the user.  In the absence of receiving any UDP notifications from Exchange, Outlook reverts to a scheduled polling of Exchange that occurs every 60 seconds, by default.

Exchange 2010 no longer issues UDP notifications to Outlook and, as a result, Outlook is then wholly dependent on its own polling frequency to retrieve new messages.  Outlook 2003 in Cached Mode and Outlook 2007/2010 are not affected by this issue because the former uses a different synchronization algorithm to send or retrieve content and Outlook 2007/2010 use an asynchronous notification process that does not rely on UDP notifications.

There are a few solutions and a workaround for the problem, as I note below.

• Implement Cached Mode for Outlook 2003 – This solution resolves the issue, as described above, but still leaves a legacy Outlook client in use.
• Upgrade to Outlook 2007/2010- We recommend that firms strongly consider upgrading the Outlook client to 2007/2010 when deploying Exchange 2010 due to all of the new features that require a newer Outlook client (OAB web-based distribution, Autodiscover, Personal Archive, etc.).  We also recommend Outlook in Cached Mode as a best practice, provided workstation hardware is sufficient for mailbox sizes.
• Reduce Polling Frequency of Outlook to Exchange – This involves the steps as outlined below to add a registry value on the Exchange 2010 CAS role to reduce the maximum polling frequency of Outlook.  While the registry value supports anywhere from 5 seconds to 2 minutes, Outlook 2003 cannot poll any more frequently than every 10 seconds.  As a result, this represents a best case scenario for Outlook 2003 in Online Mode and something where users will still likely notice delays.
  • Install Exchange 2010 Update Rollup 1.
  • On all Exchange 2010 CAS servers, navigate to  HKLM\System\CurrentControlSet\Services\MSExchangeRPC\ParametersSystem and create a REG_DWORD entitled “Maximum Polling Frequency” with a value from 5000 to 120000 (decimal value).
    • Note that, as mentioned above, configuring this to anything less than 10000 will have no additional effect on Outlook 2003.
  • Restart the Microsoft Exchange RPC Client Access service on your CAS servers.  You shouldn’t need to restart your Outlook clients but you may want to as well.

Microsoft has recently announced some new features that will be available with Exchange 2010 SP1 (anticipated in the summer timeframe of this year).  While a more detailed list is forthcoming from Microsoft, a few highlights can be found below:

• Archiving Enhancements – With SP1, you will be able to store a user’s primary mailbox in one mailbox database and that user’s Personal Archive mailbox in a different mailbox database.  This will allow administrators to leverage tiered storage for primary and archived data.  Additionally, new server side features will allow for easy back-end PST imports directly into a mailbox.  Finally, as alluded to by Microsoft previously, SP1 will include updates that will enable Personal Archive access from Outlook 2007.  Without SP1, the only methods of access for the Personal Archive are Outlook Web App 2010 and Outlook 2010.
• Management Enhancements – New capabilities will be added to both the Exchange Management Console (EMC) and Exchange Control Panel (ECP).  Specifically, the EMC will have new tools to configure/manage Retention Policies, Retention Policy Tags, Litigation Holds, DAG IP addresses and Alternate Witness Servers, recursive public folder settings and permissions, and more.  The ECP will have new tools to configure/manage Transport Rules, MailTips, Personal Archives, RBAC roles, and more.  In summary, many tasks that previously required the Exchange Management Shell will now be available through either the EMC or ECP.
• Discovery Enhancements – Multi-mailbox search will be improved by providing a Search Preview that will provide an estimated number of results (with keyword statistics as well) before exporting the desired content to the designated discovery mailbox.  This will help discovery users understand the impact of their queries and how much data to expect before actually exporting this data.  Additionally, a search de-duplication option will be provided that, when checked, will only export one instance of each unique message to the designated discovery mailbox.  This could dramatically reduce the amount of time it would take for a discovery user to review the data exported from a query.  Finally, support for annotation will be introduced so that discovery users can include notes while reviewing discovered data.
• Outlook Web App Enhancements- Outlook Web App (OWA) gets more efficient by pre-fetching message content to make reading faster and running some actions asynchronously (delete, mark read, etc.) to make them appear faster.  Additionally, various user interface improvements will be included to reduce clutter in OWA and prevent long running operations (such as attaching files) from blocking OWA access for the end user.  A new feature to anonymously share calendars via the web will be an option as well.  Finally, OWA themes return to allow users to customize the look and feel of OWA.
• ActiveSync Enhancements- Support for send as and conversation view, along with other new features will be provided.

You can read more about these new features of Exchange 2010 SP1 at http://msexchangeteam.com/archive/2010/04/07/454533.aspx.

A couple weeks ago I blogged about the XML patent infringement that Microsoft had to deal with.  As mentioned in that post, they’ve released new code that removes some of the custom XML functionality that was built into the Office 2007 system, and brings them into patent compliance.

We’ve just heard that there is at least one vendor whose product is now basically non-functional due to the code change.   This sort of problem can result in products needing to be completely re-engineered to work with the new XML limitations.

Organizations who have already implemented or are looking to implement Office 2007 should reach out to any third-party vendor who would be integrating with the Office 2007 XML format to determine compatibility with the new rules.  In addition, any custom code that has already been written would need to be tested and possibly re-written if any issues come up.

Kraft Kennedy has worked with numerous third-party vendors that integrate with Office 2007.  If you find yourself in a tough spot due to this issue, let us know and we can help walk you through the process of finding the right solution.

As you may have read, a judge recently upheld a court ruling which bans Microsoft from selling Word 2007 after January 11, 2010, due an XML patent infringement.  That was yesterday.

Today, Microsoft announced that they have released a patch which corrects the patent infringement, bringing the Office 2007 code under compliance:

The 2007 Microsoft Office OPK Master Kit Download, available on Microsoft’s OEM Partner Center, strips Word and other Office programs of custom XML editing capabilities.

“The following patch is required for the United States,” Microsoft said in a message on the site.

The 2007 Microsoft Office OPK Master Kit Download (12.9 MB) can be found at the Microsoft OEM Partner Center.  The site also says:

After this patch is installed, Word will no longer read the Custom XML elements contained within DOCX, DOCM, or XML files. These files will continue to open, but any Custom XML elements will be removed. The ability to handle custom XML markup is typically used in association with automated server based processing of Word documents. Custom XML is not typically used by most end users of Word.

Pretty quick turnaround, but I have a feeling they were working on this for a while…

As mentioned in my previous blog post about the Exchange 2010 RPC Client Access Service and the ClientAccessArray, Exchange’s dependence on the Client Access Server (CAS) role has increased dramatically in Exchange 2010.  This is because, in Exchange 2010, on-network Outlook MAPI connectivity now connects to a mailbox through the CAS role via the RPC Client Access Service.  As a result, high availability of the CAS role is crucial since any failure of CAS could affect Outlook client connectivity.  For smaller implementations or those where the limitations of native Windows Network Load Balancing (NLB) are not a major problem (please see my previous blog post for more information), NLB can work well.  The process for configuring NLB is fairly straightforward and I’ve outlined the steps below.

Preparing for NLB

Once two or more Exchange 2010 servers (each with two NICs) with the CAS role installed have been deployed, you are ready to start configuring NLB to provide high availability and load balancing.  First, you must allocate a dedicated private IP address and create an associated A record in DNS for the NLB cluster.  This IP address and name are what clients will connect to and against which the ClientAccessArray will be created.  In this blog post, I will use 10.1.240.100 and EXCHCASArray.client.local.  Please note that the IP address should be on the same subnet as the two CAS servers that will become members of the NLB cluster.

NLB can be configured either in unicast or multicast mode.  The former changes the MAC address of each NLB cluster member’s NIC to a virtual cluster MAC address, to which clients connect.  The latter allows the NICs to maintain their existing MAC addresses and adds a virtual cluster MAC address.  Unicast is the preferred method for NLB, so I will explain the process for this method in my details below.

To simplify the management of your NLB cluster members, I recommend that you name each NIC’s network connection so that it is easy to understand what function the NIC serves.  For example, as depicted below, I have named the connections “Public LAN” (used for communication with clients and servers on the network) and “NLB LAN” (used for internal NLB heartbeat).  This process should be repeated on all NLB cluster members.

The Public LAN NIC on each server should be configured normally, with an IP address, subnet mask, default gateway, DNS servers, etc.  For this example, I will use EXCHCAS01 (10.1.240.101) and EXCHCAS02 (10.1.240.103) as my two CAS servers.  The NLB LAN NIC on each server should be configured with an IP address and subnet mask only.  For this example, I will use 10.1.240.102 for EXCHCAS01 and 10.1.240.104 for EXCHCAS02.

Once the NICs have been configured, we must ensure that the binding order is configured to bind the Public LAN NIC first.  Within the Network Connections window, click Advanced, Advanced Settings and modify this if necessary.  Be sure to press the ALT key first to bring up the File menu in Windows 2008.

Configuring NLB – First Member

On each NLB cluster member, NLB must be installed.  With Windows 2008, this can be completed simply by running the command “ServerManagerCmd -i NLB” via a command prompt.  Once NLB has been installed, launch the Network Load Balancing Manager to continue the configuration process.

To create your new cluster, you can right-click Network Load Balancing Clusters or simply click Cluster, New.  In the New Cluster wizard, enter the name of the first server in the NLB cluster (for example, EXCHCAS01) and click Connect.  This will display the available NICs on the server, at which point the NLB LAN NIC should be chosen before clicking Next.

Since this is the first member of the NLB cluster, you can leave the all of the Host Parameters at their default values, as depicted below.  Please note that the Priority value should be configured as 1 for the first member.

Next we must configure the IP address and subnet mask of the NLB cluster, which is the IP address for which we created a DNS A record at the very beginning of this process.  In this example, this would be 10.1.240.100 and 255.255.255.0, respectively.

For the Cluster Parameters, we want to enter the FQDN of the DNS A record we created at the very beginning of this process (EXCHCASArray.client.local).  In addition, Unicast should be selected as the desired clustered operation mode.

The next screen allows you to configure port rules so that you can restrict what traffic is allowed across the NLB cluster IP address.  For Exchange 2010 CAS, I recommend that the default port rule of 0 – 65535 be replaced with port rules to allow only 80 (HTTP) and 443 (HTTPS).  This is especially important if servers hosting the CAS role also host other functions, such as the Hub Transport Server role.  If you require IMAP or POP3 connectivity to CAS in your environment, you will also want to add port rules for 143 and 110, respectively.  I’ve depicted the configuration of a port rule for port 80 below. 

Update: Please note that, for internally facing CAS servers front-ending MAPI traffic, you will also need to create port rules for TCP port 135 (RPC Endpoint Mapper) and TCP ports 1024-65535 (the dynamic port range for Outlook RPC access).

Once all of the desired port rules have been configured, you may click Finish to complete the configuration of the first NLB cluster member.

Let the NLB cluster converge with its first member and you should eventually see the cluster report success.

Now you can proceed with adding your second cluster member.

Configuring NLB – Second/Subsequent Member

After the configuration of the NLB cluster itself and the first NLB cluster member has been completed, you are ready to add additional members.  Provided that NLB has been installed, you can simply right-click on your NLB cluster in the Network Load Balancing Manager and click Add Host To Cluster.

Enter the name of the second NLB cluster member, for example EXCHCAS02, and click Connect.  Be sure to choose the NLB LAN NIC and click Next.

On the Host Parameters screen, ensure that the Priority is set to 2 (or as appropriate, depending on how many cluster members you have) and click Next.

Confirm that your port rules are accurate and, if they are, click Finish to add your second NLB cluster member.

Let the NLB cluster converge with the new member and, eventually, it should report success.

At this point, you have an NLB cluster with two members!

Next Steps

Before you start using your new NLB cluster for CAS functionality, you should complete two final tasks.  First, IP forwarding should be enabled on each cluster member’s NLB LAN NIC.  By default, Windows 2008 disables IP forwarding, which causes problems with NLB.  IP forwarding enabled allows, from an NLB perspective, requests sent from one NIC to be sent out the other.  IP forwarding can be enabled on your NLB LAN NIC by running netsh interface ipv4 set int “NLB LAN” forwarding=enabled from a command prompt.

Finally, you will want to configure a ClientAccessArray within Exchange 2010 to represent your new NLB cluster so that Outlook clients will not simply resolve your NLB cluster name to a participating member and store that member’s name in the MAPI profile.  Please refer to the instructions in my previous blog post for how to configure a ClientAccessArray.

One of the most anticipated new features of Microsoft’s upcoming Office 2010 release is the ability to perform simultaneous editing on documents – in other words, allowing two authors to work on a document at the same time.   Those of you who have used Microsoft Office OneNote 2007 are already familiar with the concept.   A OneNote 2007 file can be placed onto a network share, and multiple people can access the live version.   I’ve personally found OneNote’s co-authoring functionality an extremely valuable tool for note-taking during a group meeting or brainstorming business ideas.

Office 2010 brings this concept to Word, Excel and PowerPoint documents.  For a  preview of the look and feel, check out this Microsoft Office Word Team Blog post.

However, in the legal industry, the transition to allow simultaneous editing is not as simple as you may think.    Even after leading DMS products such as Open Text eDOCS DM, Autonomy iManage, or Worldox announce their compatibility with the Office 2010 platform, companies and firms won’t be able to just upgrade to 2010 and start editing documents simultaneously.   These systems are built on the idea of one person accessing a live document at a time — check it out of the system, work on it, check it back in.   So let’s assume developers did re-write their code.  Even that wouldn’t be enough for this functionality to work.  According to what we’ve heard from Microsoft, the simultaneous editing will likely require working in either a Microsoft-hosted cloud, or having SharePoint 2010 on the back-end.    This doesn’t mean that a migration from a DMS product to SharePoint is necessary, but it could mean that the DMS vendors would have to support a SharePoint document repository.  Open Text has already hinted that their releases in latter half of 2010 may support this.

As an aside, the whole idea of checking-out and checking-in documents has been ingrained into the minds of all attorneys, paralegals and administrative assistants for more than 20 years.   It won’t be easy to shake, and it might not even be accepted in the legal vertical.   Anyone know of any attorneys out there interested in this feature?

Microsoft has just announced that Exchange 2010 is now globally available!  Please read more information at the MS Exchange Team blog at http://msexchangeteam.com/archive/2009/11/09/453096.aspx. 

Exchange 2010 binaries are now available for download.

Microsoft has announced that Exchange 2010 has been released to manufacturing with expected general availability and launch to be announced at TechEd Europe 2009 in early November.  More information on Microsoft’s official announcement of Exchange 2010 can be found at the MS Exchange Team blog here.  Exchange 2010 marks a significant milestone in the development of Exchange Server.  Some of the most important features have been summarized below but many more exist that make this a compelling upgrade for all firms. 

Please note that Exchange 2007 SP2 and/or Exchange 2003 SP2 are required for coexistence with Exchange 2010 in the same Active Directory site.

• Dramatically Improved Storage Footprint and Large Mailbox Support – Changes in the underlying storage architecture allow for a 70% reduction in I/O over Exchange 2007 and a 90% reduction over Exchange 2003. This allows for more efficient usage of storage and results in the ability to store Exchange databases on slower/lower-cost disk such as SATA.  This makes Exchange not only better performing for larger mailboxes but also more cost effective.
• Native E-mail Archiving – With Exchange 2010, basic archiving features are now included natively, allowing firms to reduce the footprint of production mailboxes and improve client-side Outlook performance.  While this functionality may not be as feature-rich as third-party solutions and even though it requires a to-be-released Outlook 2010 client to support it (or OWA 2010), it does present a much needed piece of functionality that many firms have desired natively for years.
• Database Availability Groups – All of the Exchange 2007 high availability and disaster recovery methods (Local Continuous Replication, Single Copy Clustering, Cluster Continuous Replication, and Standby Continuous Replication) have been deprecated and replaced with a single concept: Database Availability Groups (DAGs).  DAGs unify the concepts of high availability and disaster recovery into a single deployment and management process, thereby simplifying it dramatically over previous versions of Exchange.
• Native eDiscovery and Compliance Features – Multi-mailbox search, legal holds, and improved retention policies all combine to increase the native capabilities of Exchange to assist with compliance processes and discovery requests.
• MailTips – Exchange can now notify users if a message violates an aspect of IT or corporate policy (sending to unauthorized third-parties or exceeding a maximum allowed message size) or if the result of sending the message may be unexpected (recipient is out of the office or a distribution list contains a large number of recipients).  This can enable users to better understand the results of sending a message and potentially reduce confusion and calls to IT.

Please refer to my three-part blog post series on Exchange 2010’s specific benefits for law firms (Part 1 can be found at http://blogs.kraftkennedy.com/index.php/2009/08/19/exchange-2010-benefits-for-law-firms-part-1-of-3/).  Check back often for additional blog posts about the new features of Exchange 2010. 

High availability and site resiliency have evolved a great deal from early versions of Exchange through Exchange 2007.  While Exchange 2007 introduced the concepts of Single Copy Clustering (SCC) and Cluster Continuous Replication (CCR) for high availability and Standby Continuous Replication (SCR) for site resiliency, each had very specific benefits and drawbacks.  CCR gradually became Microsoft’s and the industry’s preferred solution for high availability because of its robust availability capabilities but concerns about manageability, scalability, and associated storage cost were all factors when settling on a design.  SCR extended CCR technology to provide a robust and cost effective solution for site resiliency but many firms were frustrated by the configuration and database activation processes and that all administration must be completed via cmdlets.

Fortunately, Microsoft built upon the technologies introduced in Exchange 2007 and improved many of the drawbacks with features introduced in Exchange 2010.  SCC functionality has been completely deprecated and CCR/SCR/LCR have been combined and evolved into the concept of the Database Availability Group (DAG).  DAGs combine high availability and site resilience into a single technology and management point to dramatically improve configuration, management, and scalability.  In addition, while a DAG does leverage some basic elements of Windows Failover Clustering, these are merely done for membership management, heartbeat, and information distribution amongst DAG members.  At its core, Exchange 2010 is essentially no longer a cluster-aware application and the concept of the CMS has been removed.  Instead, as enabled by the new requirement that all clients connect through CAS role (see my blog post here), the Mailbox server on which a user’s database exists no longer matters and can be easily adjusted based on server availability.

A DAG is essentially a group of Mailbox servers between which an administrator wants the ability to replicate mailbox databases.  A DAG can contain up to 16 Mailbox servers across multiple sites (each with their own copy of replicated databases) and, once servers are a member of a DAG, the administrator can choose how many copies of a specific database is desired, where those copies should be stored, and how far behind (if at all) replication should lag between copies.  The administrator can also define an activation preference such that, if the server hosting the active copy of a database or the database itself fails, Exchange will attempt to bring other copies online in a specific order.

Please refer to the table below for a brief comparison of features between the high availability capabilities of SCC, CCR, and DAG.  A few additional key points to note are that high availability failovers can occur for individual databases (as opposed to whole servers in Exchange 2007), DAG management is facilitated entirely by Exchange tools, and other roles can now be hosted on the same server as the Mailbox role when configured as a DAG member.

High Availability Comparison between Exchange 2007 and Exchange 2010

There is much more to talk about with DAGs and I plan to post more information about them in the future.