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Understanding Requirements for Failover Clusters

Updated: July 8, 2010

Applies To: Windows Server 2008 R2

A failover cluster must meet certain requirements for hardware, software, and network infrastructure, and it requires the administrator to use an account with the appropriate domain permissions. The following sections provide information about these requirements.

For additional information about hardware compatibility for Windows Server 2008 R2, see http://go.microsoft.com/fwlink/?LinkId=139145.

Hardware requirements for a failover cluster

You need the following hardware in a failover cluster:

  • Servers: We recommend that you use a set of matching computers that contain the same or similar components.

    ImportantImportant
    Microsoft supports a failover cluster solution only if all the hardware components are marked as "Certified for Windows Server 2008 R2." In addition, the complete configuration (servers, network, and storage) must pass all tests in the Validate a Configuration Wizard, which is included in the Failover Cluster Manager snap-in.

    For information about hardware compatibility for Windows Server 2008 R2, see http://go.microsoft.com/fwlink/?LinkId=139145.

    For information about the maximum number of servers that you can have in a failover cluster, see http://go.microsoft.com/fwlink/?LinkId=139146.

  • Network adapters and cable (for network communication): The network hardware, like other components in the failover cluster solution, must be marked as "Certified for Windows Server 2008 R2." If you use iSCSI, your network adapters should be dedicated to either network communication or iSCSI, not both.

    In the network infrastructure that connects your cluster nodes, avoid having single points of failure. There are multiple ways of accomplishing this. You can connect your cluster nodes by multiple, distinct networks. Alternatively, you can connect your cluster nodes with one network that is constructed with teamed network adapters, redundant switches, redundant routers, or similar hardware that removes single points of failure.

    noteNote
    If you connect cluster nodes with a single network, the network will pass the redundancy requirement in the Validate a Configuration Wizard. However, the report from the wizard will include a warning that the network should not have single points of failure.

    For more details about the network configuration required for a failover cluster, see Network infrastructure and domain account requirements for a failover cluster, later in this topic.

  • Device controllers or appropriate adapters for the storage:

    • For Serial Attached SCSI or Fibre Channel: If you are using Serial Attached SCSI or Fibre Channel, in all clustered servers, all components of the storage stack should be identical. It is required that the multipath I/O (MPIO) software and Device Specific Module (DSM) software components be identical.  It is recommended that the mass-storage device controllers—that is, the host bus adapter (HBA), HBA drivers, and HBA firmware—that are attached to cluster storage be identical. If you use dissimilar HBAs, you should verify with the storage vendor that you are following their supported or recommended configurations.

      noteNote
      With Windows Server 2008 R2, you cannot use parallel SCSI to connect the storage to the clustered servers. This was also true for Windows Server 2008.

    • For iSCSI: If you are using iSCSI, each clustered server should have one or more network adapters or host bus adapters that are dedicated to the cluster storage. The network you use for iSCSI should not be used for network communication. In all clustered servers, the network adapters you use to connect to the iSCSI storage target should be identical, and we recommend that you use Gigabit Ethernet or higher.

      For iSCSI, you cannot use teamed network adapters, because they are not supported with iSCSI.

      For more information about iSCSI, see the iSCSI FAQ on the Microsoft Web site (http://go.microsoft.com/fwlink/?LinkId=61375).

  • Storage: You must use shared storage that is compatible with Windows Server 2008 R2.

    In most cases, the storage should contain multiple, separate disks (LUNs) that are configured at the hardware level. For some clusters, one disk functions as the disk witness (described at the end of this subsection). Other disks contain the files required for the clustered services or applications. Storage requirements include the following:

    • To use the native disk support included in failover clustering, use basic disks, not dynamic disks.

    • We recommend that you format the partitions with NTFS. If you have a disk witness or use Cluster Shared Volumes, the partition for each of those must be NTFS.

      For Cluster Shared Volumes, there are no special requirements other than the requirement for NTFS. For more information about Cluster Shared Volumes, see Understanding Cluster Shared Volumes in a Failover Cluster.

    • For the partition style of the disk, you can use either master boot record (MBR) or GUID partition table (GPT).

    A disk witness is a disk in the cluster storage that is designated to hold a copy of the cluster configuration database. A failover cluster has a disk witness only if this is specified as part of the quorum configuration. For more information, see Understanding Quorum Configurations in a Failover Cluster.

Deploying storage area networks with failover clusters

When deploying a storage area network (SAN) with a failover cluster, follow these guidelines:

  • Confirm compatibility of the storage: Confirm with manufacturers and vendors that the storage, including drivers, firmware, and software used for the storage, are compatible with failover clusters in Windows Server 2008 R2.

    ImportantImportant
    Storage that was compatible with server clusters in Windows Server 2003 might not be compatible with failover clusters in Windows Server 2008 R2. Contact your vendor to ensure that your storage is compatible with failover clusters in Windows Server 2008 R2.

    Failover clusters include the following new requirements for storage:

    • Improvements in failover clusters (as compared to server clusters in Windows Server 2003) require that the storage respond correctly to specific SCSI commands. To confirm that your storage is compatible, run the Validate a Configuration Wizard. In addition, you can contact the storage vendor.

    • The miniport driver used for the storage must work with the Microsoft Storport storage driver.

  • Isolate storage devices, one cluster per device: Servers from different clusters must not be able to access the same storage devices. In most cases, a LUN used for one set of cluster servers should be isolated from all other servers through LUN masking or zoning.

  • Consider using multipath I/O software: In a highly available storage fabric, you can deploy failover clusters with multiple host bus adapters by using multipath I/O software. This provides the highest level of redundancy and availability. For Windows Server 2008 R2, your multipath solution must be based on Microsoft Multipath I/O (MPIO). Your hardware vendor will usually supply an MPIO device-specific module (DSM) for your hardware, although Windows Server 2008 R2 includes one or more DSMs as part of the operating system.

    ImportantImportant
    Host bus adapters and multipath I/O software can be very version sensitive. If you are implementing a multipath solution for your cluster, you should work closely with your hardware vendor to choose the correct adapters, firmware, and software for Windows Server 2008 R2.

Software requirements for a failover cluster

All the servers in a failover cluster must either run the x64-based version or the Itanium architecture-based version of Windows Server 2008 R2 (nodes within a single failover cluster cannot run different versions).

All the servers should have the same software updates (patches) and service packs.

The Failover Clustering feature is included in server products such as Windows Server 2008 R2 Enterprise and Windows Server 2008 R2 Datacenter. The Failover Clustering feature is not included in Windows Server 2008 R2 Standard or Windows Web Server 2008 R2.

Network infrastructure and domain account requirements for a failover cluster

You will need the following network infrastructure for a failover cluster and an administrative account with the following domain permissions:

  • Network settings and IP addresses: When you use identical network adapters for a network, also use identical communication settings on those adapters (for example, Speed, Duplex Mode, Flow Control, and Media Type). Also, compare settings between the network adapter and the switch it connects to and make sure that no settings are in conflict.

    If you have private networks that are not routed to the rest of your network infrastructure, ensure that each of these private networks uses a unique subnet. This is necessary even if you give each network adapter a unique IP address. For example, if you have two cluster nodes in a central office that uses one physical network, and two more nodes in a branch office that uses a separate physical network, do not specify 10.0.0.0/24 for both networks, even if you give each adapter a unique IP address.

    For more information about the network adapters, see Hardware Requirements for a Failover Cluster, earlier in this topic.

  • DNS: The servers in the cluster must be using Domain Name System (DNS) for name resolution. The DNS dynamic update protocol can be used.

  • Domain role: All servers in the cluster must be in the same Active Directory domain. As a best practice, all clustered servers should have the same domain role (either member server or domain controller). The recommended role is member server.

  • Domain controllers: We recommend that your clustered servers be member servers. If they are, other servers will be the domain controllers in the domain that contains your failover cluster.

  • Clients: There are no specific requirements for clients, other than the obvious requirements for connectivity and compatibility: the clients must be able to connect to the clustered servers, and they must run software that is compatible with the services offered by the clustered servers.

  • Account for administering the cluster: When you first create a cluster or add servers to it, you must be logged on to the domain with an account that has administrator rights and permissions on all servers in that cluster. The account does not need to be a Domain Admins account—it can be a Domain Users account that is in the Administrators group on each clustered server. In addition, if the account is not a Domain Admins account, the account (or the group that the account is a member of) must be delegated Create Computer Objects and Read All Properties permissions in the domain. For more information, see Failover Cluster Step-by-Step Guide: Configuring Accounts in Active Directory (http://go.microsoft.com/fwlink/?LinkId=139147).

    noteNote
    There is a change in the way the Cluster service runs in Windows Server 2008 R2, as compared to Windows Server 2003. In Windows Server 2008 R2, there is no Cluster service account. Instead, the Cluster service automatically runs in a special context that provides the specific permissions and privileges necessary for the service (similar to the local system context, but with reduced privileges).

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