Windows Server 2008 Failover Clustering – Storage Changes

In a previous blog, I talked a little bit about some of the major changes to disk storage for Windows Server 2008 Failover Clustering. Now, while I wait for dinner to cook, is a good time to cover some of the changes.

  • 2TB Limit- The biggest change, in my opinion, has to be elimination of the Master Boot Record (MBR) requirement for clustered disks. MBR forced a limitation to the physical disk resource size of 2TB. Now, Windows Server 2008 supports the use of GUID (sometimes called Global) Partition Table (GPT) which allows up to 16 Exabyte. The practical limit is really around 160-200 TB based on today’s technology. Keep in mind that just because you can do it doesn’t mean you should do it. Can you imagine how long it would take to degrag a 100TB disk? How about reindexing it? How about chkdsk?

  • SCSI Bus Resets – In Windows Server 2003 Server Clustering, SCSI bus resets are used to break disk reservations forcing it to become disconnected so that another controller can take control of the disks. The problem with SCSI bus resets is that they require all devices on the same bus to lose their connection. These resets were not exactly warmly received by the disks that were impacted without any reason for it. In Windows Server 2008 Failover Clustering, SCSI bus resets are no longer used as persistent reservations are now required.

  • Persistent Reservations – WIndows Server 2008 Failover Clustering supports the use of persistent reservations. This means that directly attached SCSI storage will no longer be supported in 2008 for Failover Clustering. Serially Attached Storage (SAS), Fiber Channel, and iSCSI will be the only supported technology. However, not all vendors support persistent reservations, so this will be a problem as organizations move to Windows Server 2008 Failover Clustering without full and proper testing.

  • Maintenance Mode – In maintenance mode allows administrators to gain exclusive control to clustered disks

  • Disk Signatures – In Windows Server 2003 (and earlier), administrators would come to our classes at and would cringe whenver we talked about disk signatures. I even had one burst into tears from reliving past stress. OK, maybe not real tears. Anyways, clustering used disk signatures to identify each clustered disk. The disk signature, at sector 0, is often an issue in disaster recovery scenarios (in class I show how to totally get around disk signature issues). To make it easier, Failover Clustering makes use of SCSI Inquiry Data is often written to a LUN by a SAN. In the event the disk signature gets out of whack, the disk signature can be reset once the disk has been verified by the SCSI Inquiry Data. If for some reason, both the disk signature and the SCSI Inquiry Data are not available or are misconfigured/corrupted, an administrator can a Repair button is available on the Physical Disk Resource properties general page. The Repair button can be used to point the actual disk to the resource.

  • Disk Management – The virtual disk service (VDS) APIs first became available with 2003 R2. Using the disk tools in Windows Server 2003 R2 (and now 2008), an administrator can build, delete, and extend volumes in the SAN.

All in all, there have been some pretty significant changes when it comes to the way Windows Server 2008 Failover Clusters work with disk storage.


Windows Server 2008 Failover Clustering – The New Quorum Model

One of the big changes in Windows Server 2008 Failover Clustering is the new quorum model. In Windows Server 2003, we had only two choices, either the single disk quorum that has been around since NT 4.0 or Majority Node Set (MNS). Actually, there are three if you consider MNS with the File Share Witness (FSW) as a separate option.

In Windows Server 2008 Failover Clustering, administrators now have four choices on how to implement the quorum.

  • One option is to use Node majority. In this option, a vote is given to each node of the cluster and the cluster will continue to run so long as there are a majority of nodes up and running.

  • A second option is to use both the nodes and the standard quorum disk. In this option, a common option for two node clusters, each node gets a vote and the quorum, now called a witness disk) also gets a vote. So long as two of the three are running, the cluster will continue. In this situation, the cluster can actually lost the witness disk and still run.

  • A third option is to use the classic/legacy model and assign a vote to the witness disk only. This type of quroum equates to the well known, tried, and true model that has been used for years.

  • A fourth option, is, of course, to use the MNS model with a file share witness.

It has been a few days since I have seen the GUI, so I can’t tell you off the top of my head which order they appear in within the GUI.

Two notes that caught my attention the other day when talking about these options is that it is not possible to use DFS as the file share witness and with changes to the quorum there aren’t any checkpoints so there is no longer a need for the -resetquorumlog switch on starting the cluster service.


Windows Server 2008 Failover Clustering – Top Questions

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


TechEd and Windows Server 2008 Failover Clustering

I am sure there are many of you that have a million questions about Windows Server 2003 clustering and Windows Server 2008 failover clustering.

Guess what? You can ask away at the booth at TechEd. Three of the Windows Server – Clustering MVPs will be rotating along with some Microsoft personnel at the Failover Clustering booth. I will be working it a few hours a day during TechEd along with fellow MVPs Ryan Sokowloski and Rodney Fournier.

 From my understanding, we will be in the TLC Yellow section next to the Datacenter Edition booth.

Come say hello and feel free to ask us questions.


eLearning – Windows Server 2008 Failover Clustering

Microsoft recently published a two hours online course on Failover Clustering for Windows Server 2008 (formerly known as Longhorn).

You can access this content here and for $39.99, you can spend as much time as you want for the next three years reviewing the content.

This course, Course 6051: Implementing High Availability and Virtualization in Windows Server 2008 is part of a larger group of courses that can be purchased as a group, or you can purchase this individual course separate from any other eLearning course.

Rod Fournier and I are working on very similar material, with much more depth for our course. However, we will not be releasing it until Windows Server 2008 is released to manufacturing. Look for more information here as Windows Server 2008 comes closer to release.

Great Deals @!