The number one question by far at the cluster booth during TechEd was, "What are the differences between Windows Server 2003 Server Clustering and Windows Server 2008 Failover Clustering?"
The major differences that I can discuss off the top of my head include:
Service Account - There is no longer a need for a service account for the cluster service. It now uses the local system account.
Validate - The new validate tool tests the complete configuration and provides a report of items that need to be fixed or a nice report saying that the cluster passed. If the cluster passes the validate test tool, it will be fully supported by Microsoft.
Quroum - The quroum has changed considerably. I will discuss these changes in a blog in the next few days.
SAN Support - This also deserves its own blog entry. Basically, there is no longer a 2TB disk limit imposed by MBR formatting. 2008 supports GPT so you can get 16 Exabyte, theoretically, but really only about 160 TB or so based on today's tecnology. Also the nodes can use the virtual storage API to create LUNs if the storage vendor supports the APIs. Also, the new clustering technology uses persistent reservations, which is not supported by many current iSCSI implementations. Most iSCSI vendors are working to update to meet there requirements.
Configurable Heartbeat timeout - There is no longer a 500ms roundtrip limitation for heartbeat communications.
OR - Networking - The addition of the OR logic is a huge change in my opinion as now we can use the OR with two TCP/IP addresses and the addresses can be from different subnets. This option enables geo clustering without the use of a VLAN. Yes, you got that right, no more need for a VLAN for geo clustering.
Migration - Yes, the new 2008 is x64. You can not combine 32 bit and 64 bit nodes, so you can't do a rolling upgrade from 2003 to 2008. All upgrades will have to be migrations.
Scoping - One of the complaints with 2003 was that if you had multiple file share virtual servers and they were on the same physical node, all of the shares would show up in all of the virtual servers. Now scoping allows control so these other shares are not visible.
Ease of Use - The ability to create a cluster group with its appropriate resources takes about 5 screens and you are done. It is incredibly simple to cluster resources now. I will provide a comparison in a blog in the next week or two.
The second most asked question appeared (yeah, yeah, I didn't bother actually tracking) was about Virtual Server 2005 R2 and whether virtual servers could be clustered. The answer is yes, they can be clustered. The process is called Host clustering since the host machines are clustered, and the virtualized servers can be moved (or failed) over to other hosts. You can read all about it at http://technet2.microsoft.com/windowsserver/en/library/9a3de6d0-c820-41ac-860c-de950d271f8d1033.mspx?mfr=true.