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A key principle in achieving continuous availability is reducing single points of failure and ensuring that redundant components complete failover in a nondisruptive fashion. As discussed in Windows Server availability, failover can be disruptive to applications and interrupt business continuity. Therefore, providing a consistent, resilient storage connection across redundant storage appliances to Windows Server and applications such as SQL Server can reduce failover events and increase availability.
Dell metro node adds a storage virtualization layer to the storage infrastructure. When the metro node cluster is in place, storage is presented from one or more underlying arrays. From this pool of storage, virtual volumes are created in metro node. These virtual volumes have their own Logical Unit (LUN ID) and World Wide Name (WWN), which gives each its own identity and makes them unique from a host or server perspective. The virtual volume is then presented to the host and appears like any other volume. The key benefit of a virtual volume is that it provides a consistent identity and connectivity, regardless of the storage appliance on which the data resides. This allows data to move between arrays, and the creation and deletion of mirrored volumes across two arrays, without requiring any outage from an application point of view. The virtual volume can be configured for true active/active synchronous replication either locally or over metro distances with multisite dual access. This provides zero RPO and RTO for storage.
Virtualizing the storage details behind the metro node cluster ensures that Windows Server, or any storage consumer, has a consistent, reliable storage connection across one or more arrays. This includes PowerVault appliances, other Dell storage arrays, or any array type supported by metro node, in one or more locations. This eliminates downtime due to data migrations, storage appliance upgrades, and unplanned failures.
When virtualizing PowerVault storage behind metro node, PowerVault advanced storage features such as snapshots and asynchronous replication remain available.
Each metro node cluster consists of two hardware nodes based on the Dell R640 PowerEdge server platform. The dual node architecture provides resiliency within the metro node architecture by providing redundancy of every metro node hardware component.
In addition to resiliency and virtualization, another key component to reducing or eliminating downtime is the time required to make a decision when an event occurs. This is known as the decision time objective (DTO). Other architectures may not support automated failover or resynchronization and therefore require key decisions to be made by business stakeholders, weighing the effort required to fail over and then to resynchronize the data and failback. These decisions and approvals take time and increase down time. Metro node handles this decision automatically allowing for a zero DTO and therefore reducing or eliminating downtime.