Creating a stretched cluster. Dell AX-640, AX-6515, AX-740XD, AX-7525

Add to My manuals
25 Pages


Creating a stretched cluster. Dell AX-640, AX-6515, AX-740XD, AX-7525 | Manualzz


Creating a stretched cluster

This chapter presents the following topics:




Cluster creation


Storage efficiency



This section outlines the steps that are needed for configuring a stretched cluster. Complete the network configuration on all nodes for the network topology applicable to you. A sample IP address schema is provided for both supported network topologies in the previous section of this guide. Consider these points before you begin:

● Ensure management IPs of all nodes are reachable from any host

● Ensure static routes are configured on all hosts for inter-site communication using the Replica network

● Ensure all nodes from Site A can reach corresponding Replica IPs on Site B using the Replica path


Test-Cluster is a fundamental function that is needed to ensure that the cluster to be created meets Microsoft's recommendations regarding Failover Clustering. It also ensures that your hardware and settings are compatible. Run Test-

Cluster with all nodes and include All Tests (namely, 'Storage Spaces Direct', 'Inventory', 'Network' and 'System Configuration').

Ensure there are test-cluster passes without warnings for the 'High Throughput Configuration', while 'Basic Configuration' will receive a warning as mentioned in the previous section of this guide.

Cluster creation

This section looks at creating a cluster using PowerShell cmdlets.

Manual cluster creation

Once Test-Cluster completes successfully, use the New-Cluster cmdlet to create a new stretched cluster. Because the nodes specified are part of different IP schemas, Enable-ClusterS2D understands that the cluster is part of a multi-site topology. It automatically creates two storage pools and corresponding ClusterPerformanceHistory volumes and their replica volumes.

After a cluster is created, you will see a warning similar to the one shown below. This is an expected behavior.

No matching network interface found for resource 'Cluster IP Address' IP address '' (return code was '5035'). If your cluster nodes span different subnets, this may be normal.

Configure cluster witness and Enable Storage Spaces Direct on the cluster.

NOTE: Cluster witness can be either on a tertiary site or on Azure Cloud. Ensure that the "Storage Replica" feature is installed on all nodes in the cluster.

14 Creating a stretched cluster

If Sites and Services with IP Subnets are configured on Active Directory, Failover Cluster Manager correctly shows a node to

Site mapping, under Cluster Name >> Nodes .

The following is a sample image of IP subnets defined in an Active Directory:

Figure 5. IP subnets in an Active Directory

If both sites are in the same IP network, use the New-ClusterFaultDomain cmdlet to define the two site names. Site names defined using New-ClusterFaultDomain override the names given in Active Directory.

The following is a sample image of how sites appears in Failover Cluster Manager:

Figure 6. Sites in Failover Cluster Manager

Once a cluster is created, use Failover Cluster Manager to rename the cluster networks.

Creating a stretched cluster 15

Figure 7. Cluster networks


Replication-enabled volumes can be created using a combination of PowerShell and Failover Cluster Manager or by using

Windows Admin Center.

NOTE: Install Storage Replica Module for Windows PowerShell (RSAT-Storage-Replica) on the management node with

Desktop Experience that is used for installing Windows Admin Center and Failover Cluster Manager to access the cluster.

For each replica-enabled volume, you need a corresponding log volume on both sites (with a minimum of 8 GB in size) and an equivalent replica volume on the secondary site. The log volume is used to serialize writes for replication.

The following table shows the volumes that are needed to create a 1 TB replica volume:

Table 6. Volumes in a 1 TB replica volume

Site A




1 TB

40 GB



500 GB

40 GB

Site B






1 TB

40 GB

500 GB

40 GB


Appendix A

for the correct PowerShell Cmdlets and Failover Cluster Manager steps to create the volumes shown in this table. It is recommended that you create two-way mirrors for all volumes to improve write performance and capacity efficiency.

NOTE: For Asynchronous Replication, the RPO can be set as low as 30 seconds.

For a planned site failure, when the volume replication direction is reversed, the disk reservations on the secondary site for

Replica Volume and Replica-log volumes are removed and moved to the primary site. Source Data and Source Log volumes are given the disk reservations and become active on the secondary site. After 10 minutes, the virtual machines residing on the primary site associated with the migrated volume automatically Live Migrate to the secondary site.

16 Creating a stretched cluster

Storage efficiency

Due to high I/Os on the underlying disks, stretched clusters require an underlying infrastructure capable of delivering high I/Os with low latency. Dell Technologies recommends all-flash configurations for stretched cluster deployments.

All-flash configurations do not have a cache tier. The following table shows the difference in storage efficiency for a two-way and three-way mirror created on a single site and stretched cluster environment:

Table 7. Storage efficiency differences

Two-Way Mirror

Single site

Stretched cluster



Three-Way Mirror




This cmdlet validates a potential replication partnership. The cmdlet:

● Measures bandwidth and round trip latency

● Estimates initial sync time

● Verifies that source and destination volumes exist

● Verifies that there is sufficient physical memory to run replication

NOTE: The file server feature has to be enabled on the nodes to run this cmdlet.

Keep the generated report for future reference.

For more information about this cmdlet, see Test-SRTopology .

Creating a stretched cluster 17


Related manuals