Node Majority in Visual Studio .NET

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Node majority does not use any witness disk or le share witness and instead relies on at least half the number of nodes being available Votes are assigned only to the nodes in the cluster The cluster must have at least
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three nodes To be exact, the number of nodes that must be present is half the total number of nodes rounded down, plus 1 in a four-node cluster, at least three nodes must be present; in a ve-node cluster, at least three nodes must be present; in a seven-node cluster, at least four nodes must be present, and so on This con guration is recommended when there are an odd number of nodes, as shown in Figure 18-17
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FIGURE 18-17 The cluster can survive if the majority number of nodes are present
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Node and Disk Majority
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In node and disk majority con guration, the witness disk and each node have one vote This con guration can sustain availability if half the nodes fail, providing the witness disk is present This means a six-node cluster could have three nodes unavailable, providing the witness disk is online If the witness disk is not online, the number of supported failures is half the number of nodes (rounded up) minus 1, so a six-node cluster with an unavailable witness disk can support only two nodes being unavailable (shown in Figure 18-18) Notice there are ve votes and, in both situations, three votes are present This con guration is recommended for an even number of nodes where shared storage is available
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FIGURE 18-18 The cluster can survive if the majority number of nodes are present; either
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two nodes and the witness disk or three nodes are required with the witness disk unavailable
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Failover Clustering
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Node and File Share Majority
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Node and le share majority works the same as Node and Disk Majority, but instead of a shared witness disk holding a copy of the cluster con guration Registry, a le share witness is used containing just a token le, as shown in Figure 18-19 This is recommended for con gurations where no shared storage is available, and you have two nodes
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FIGURE 18-19 The cluster can survive if the majority number of nodes are present; either
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two nodes and the le share witness or three nodes are required with the le share witness unavailable
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No Majority: Disk Only
In the disk-only model, the number of available nodes does not matter, and the cluster can sustain failure of all nodes except 1, as long as the witness disk is available (The witness disk has the only vote) This con guration relies 100% on the witness disk, which introduces a single point of failure, as all nodes could be available, but if the witness disk goes of ine, the cluster is stopped, as shown in Figure 18-20 This model is never recommended because of the single point of failure that the reliance on the witness disk introduces
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Witness Disk
Witness s Disk
FIGURE 18-20 When using the disk-only model, only one node is required with the witness
disk; if the witness disk is unavailable, however, the cluster is unavailable, no matter how many nodes are running (even all, as shown on the right)
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Networking and Security Enhancements
A number of network enhancements are introduced for clusters in Windows Server 2008 First, DHCP is now enabled for all IP components of the cluster Previously, the cluster IP and dedicated IPs had to be statically assigned With Windows Server 2008, all addresses are DHCPgenerated; the default process when creating a cluster is, if the network adapter is con gured for DHCP, you are not prompted for an address for the cluster The cluster also uses DHCP (Although this can be changed) The use of DHCP has good points and bad points DHCP is an easier con guration for the cluster; however, the cluster then becomes dependent on DHCP being available and effectively introduces a single point of failure due to the DHCP reliance This depends on your organization, but it s certainly welcome in some environments IPv6 is fully supported and can be used for client access to the cluster and for inter-node communication The dependency on NetBIOS has been removed with Windows Server 2008 failover clustering This offers simpler SMB traf c transportation, no more WINS and NetBIOS name resolution broadcasting, and a standardized name resolution on DNS, as with most Windows components Kerberos is now mandatory for failover clustering, with NTLM no longer used When Kerberos is combined with secure TCP sessionoriented protocols instead of datagram (UDP) RPC protocols and IPsec improvements, you have a far more secure cluster implementation than with 2003 However, there is no compatibility between 2003 and 2008 clusters The security changes break compatibility at an API level A mix of 2003 and 2008 nodes is not possible in a cluster, and the cluster management tools are not interoperable You can t manage a 2003 cluster from the 2008 failover cluster management MMC snap-in, and you can t manage a 2008 cluster from the 2003 cluster MMC snap-in Customer feedback to Microsoft indicated that the improvements in security were more important than interoperability Clusters can have multiple IP addresses A cluster can stay up, providing any one of the IP addresses is still available (known as an OR dependency), instead of requiring all; this is important when considering the next change in clustering One of the biggest changes is the new stretched cluster enhancements that allow cluster nodes to be in separate IP subnets, which enables globally dispersed clusters (multisite cluster) with cluster