By Robin Smith 
Global Active Device is a storage technology designed to help organizations maintain continuous access to critical data across multiple storage systems. Developed by Hitachi Vantara, Global-Active Device (GAD) uses synchronous remote replication to maintain paired copies of data and supports an active-active storage architecture.
For businesses running databases, virtual machines, financial applications, healthcare systems, and other mission-critical workloads, storage availability is closely connected to business continuity. A conventional backup can protect data after a failure, but it does not necessarily keep applications running during an infrastructure outage. Global Active Device addresses this challenge by allowing supported storage environments to work together so workloads can continue accessing data when certain storage or path failures occur.
Global Active Device, commonly known as GAD, is a Hitachi Vantara storage replication technology that provides synchronous, remote, active-active replication between supported storage systems.
In a GAD configuration, primary and secondary volumes are paired between two storage systems. The host can see the paired volumes as a single logical volume, while both storage systems receive the same data from the host.
Unlike a conventional primary-secondary replication model, GAD allows read/write operations on both sides while the pair is operating in its active state. This is one of the characteristics that makes it useful for high-availability environments.
The technology is particularly relevant when an organization wants to reduce storage-related downtime and maintain access to applications during certain infrastructure failures.
A basic GAD architecture consists of two storage systems connected through remote replication paths.
The primary storage system contains the primary volume, while the secondary system contains the paired secondary volume. Data written by the host is synchronously replicated between the two storage environments.
A simplified model looks like this:
Both storage systems maintain synchronized copies of the relevant data. Host multipathing and other components can provide alternative access paths when a storage system or path becomes unavailable.
According to Hitachi Vantara’s documentation, when the host cannot access the primary or secondary volume, alternate path software can redirect I/O to an appropriate volume without requiring changes to the host application.
This architecture is designed to reduce the dependency on a single storage system.
The most important distinction is its active-active approach.
In a traditional replication arrangement, one storage system may handle production workloads while another maintains a replicated copy for recovery. The secondary system may only become active after a failure or planned recovery operation.
GAD is designed differently. Both sides of the replication pair can remain active, allowing data to be accessed from either storage environment according to the configuration.
Hitachi’s documentation describes GAD as providing continuous server I/O during certain failures, server failover and failback without storage impact, and virtual-machine migration without storage impact.
This makes GAD useful for organizations where maintaining application availability is a higher priority than simply having a backup copy.
A successful GAD implementation involves more than two storage arrays. Several components work together to maintain availability and consistent operation.
The architecture uses two supported storage systems that maintain the replicated volumes.
The systems can be positioned at separate locations, depending on the organization’s design and the supported configuration.
The primary and secondary volumes form a replication pair.
The data on these volumes is maintained synchronously so that the secondary copy can support availability requirements when a failure occurs.
Hitachi documentation explains that the primary and secondary volumes can be assigned the same virtual LDEV number through virtual storage machines, allowing the host to treat them as a single logical volume.
The quorum disk is one of the most important components in a GAD configuration.
It acts as a heartbeat mechanism between the storage systems and helps determine which system should continue processing server I/O during certain communication or storage failures.
The quorum can be located in an external storage system, and Hitachi recommends careful placement to improve fault tolerance. Its purpose is especially important in avoiding conflicting decisions when the two storage systems cannot communicate normally.
A virtual storage machine, or VSM, helps provide consistent storage-system identities and configurations across the GAD environment.
Hitachi’s current documentation explains that a VSM can be configured on the secondary storage system using information from the primary system.
Multipathing provides multiple paths between hosts and storage resources.
If one path becomes unavailable, the host can use an alternative path. The exact multipathing technology depends on the environment and configuration. Hitachi documentation notes that active/active alternate paths can be used at campus distances, while certain metro configurations require appropriate multipathing software such as ALUA or Hitachi Dynamic Link Manager.
One of the main reasons organizations consider GAD is the ability to maintain access to data during certain storage failures.
If one storage system becomes inaccessible, the architecture can allow I/O to continue through the available storage resources, subject to the configuration and failure scenario.
Because GAD uses synchronous replication, changes are maintained between the paired volumes rather than relying on a delayed replication schedule.
This makes the technology appropriate for workloads where maintaining closely synchronized copies is important.
The active-active model can provide greater flexibility than a traditional passive secondary environment.
Both storage sides can participate in workload operations, making the architecture useful for certain maintenance, migration, and availability scenarios.
GAD supports failover and failback capabilities designed to maintain application access during supported storage failures.
Hitachi specifically lists server failover and failback without storage impact among the technology’s benefits.
GAD can also support moving virtual machines between storage environments without requiring the storage itself to be migrated in the conventional manner.
This can be valuable during planned maintenance, infrastructure upgrades, or workload balancing.
Business continuity is broader than storage replication.
A complete continuity strategy may include:
- High-availability infrastructure
- Storage replication
- Application clustering
- Network redundancy
- Independent backups
- Disaster recovery procedures
- Monitoring
- Failover testing
- Documented recovery processes
GAD can form an important storage layer within this architecture, but it should not be treated as the entire disaster recovery strategy.
For example, if a file is accidentally deleted or data becomes corrupted, synchronous replication can replicate that change to the other storage system. An independent backup or point-in-time recovery mechanism may therefore still be necessary.
Hitachi also notes that backup and point-in-time copies remain important for protecting against corruption, errors, or malicious activity.
Understanding the difference between replication approaches is useful when selecting a storage architecture.
| Feature | Global Active Device | Traditional Primary-Secondary Replication |
| Replication | Synchronous | Can be synchronous or asynchronous |
| Storage model | Active-active | Commonly active-passive |
| Data consistency | Closely synchronized | Depends on replication type |
| Failover | Designed for supported automatic/managed scenarios | Often requires recovery procedures |
| Workload mobility | Supported in appropriate configurations | Usually more limited |
| Main objective | High availability and continuous access | Data protection and recovery |
This does not mean that GAD replaces traditional disaster recovery technologies. Instead, it can complement them.
For long-distance disaster recovery, asynchronous replication may sometimes be more practical because it does not require every write to wait for remote acknowledgment.
Mission-Critical Databases
Financial systems, ERP platforms, CRM databases, and other enterprise applications can benefit from storage architectures designed to reduce infrastructure-related downtime.
Financial Services
Banks and financial institutions often operate applications where service interruptions can affect transactions, customers, and internal operations.
An active-active storage architecture can help reduce the impact of certain storage failures.
Healthcare
Healthcare organizations rely on information systems for clinical and administrative operations. Maintaining access to critical storage can therefore be an important component of infrastructure resilience.
Virtualized Data Centers
Virtual machines depend on reliable storage. A storage outage can potentially affect many workloads at once.
GAD can provide an additional layer of resilience for supported virtualized environments.
Planned Maintenance
High availability is not only about unexpected disasters. Organizations also need to perform maintenance, upgrades, migrations, and infrastructure changes.
GAD can support workload mobility and non-disruptive operations in appropriate configurations, helping organizations reduce the operational impact of planned maintenance.
It is important to distinguish high availability from disaster recovery.
High availability aims to keep services running when individual components fail.
Disaster recovery focuses on restoring operations after a larger disruption, such as a site failure or major infrastructure incident.
GAD can contribute to both objectives, but organizations should build a broader recovery strategy around it.
A mature disaster recovery plan should address:
- Data replication
- Application dependencies
- Network connectivity
- Backup and restore
- Recovery procedures
- User access
- Monitoring
- Failover testing
This approach reduces the risk of depending on a single technology for every failure scenario.
Before implementing Global Active Device, organizations should carefully evaluate their infrastructure.
Network Performance
Synchronous replication depends heavily on communication between storage systems. Network latency, bandwidth, and reliability can therefore affect the design.
Hitachi’s technical guidance emphasizes planning physical paths according to workload requirements and ensuring sufficient bandwidth for data transfers under expected conditions.
Distance Between Sites
The distance between storage environments matters because synchronous replication requires timely communication.
Organizations should verify the supported distance and latency requirements for their specific storage models, software versions, and workloads instead of relying on a generic distance figure.
Quorum Placement
Quorum placement deserves particular attention.
A quorum located independently from the primary and secondary storage environments can improve fault isolation. Hitachi technical guidance recommends considering a third site for the quorum device to improve fault tolerance.
Storage Capacity
Both storage environments need adequate capacity for replicated workloads.
Capacity planning should include current utilization, expected growth, snapshots or other data storage, and operational overhead.
Application Dependencies
Storage availability alone does not guarantee application availability.
Databases, application servers, virtual machines, networks, DNS, authentication, and other dependencies should be considered when designing the complete high-availability architecture.
Global Active Device provides significant capabilities, but it also introduces additional infrastructure and management requirements.
Organizations should consider:
- Storage hardware requirements
- Replication bandwidth
- Network latency
- Multipathing configuration
- Quorum infrastructure
- Licensing
- Operational complexity
- Monitoring
- Testing
- Application compatibility
- Backup requirements
Synchronous replication can also create additional network and performance considerations compared with asynchronous replication.
For this reason, GAD should be selected after evaluating actual workload requirements rather than simply because active-active storage sounds attractive.
A successful deployment starts with careful planning.
Identify Critical Workloads
Determine which applications genuinely require continuous or near-continuous availability. Not every workload needs the same level of protection.
Define RTO and RPO
Establish realistic recovery objectives before designing the storage environment.
Plan Redundant Paths
Redundant physical and logical paths can reduce the risk of a single connection becoming a point of failure.
Protect the Quorum
Quorum placement should be designed carefully so that it remains available during likely failure scenarios.
Monitor Replication Health
Regular monitoring can identify replication problems, path failures, capacity constraints, or other issues before they become major incidents.
Test Failover
A high-availability design should be tested under controlled conditions. Testing helps verify that hosts, applications, networks, multipathing, and storage behave as expected.
Maintain Independent Backups
Replication is not a replacement for backup. Maintain separate recovery mechanisms for accidental deletion, corruption, ransomware, and other logical threats.
Global Active Device provides an active-active storage architecture designed to keep critical data available across supported storage environments. Through synchronous replication, redundant paths, quorum-based coordination, and failover capabilities, it can help organizations reduce the impact of storage-related failures.
For the strongest results, GAD should be implemented as part of a broader business-continuity strategy that also includes backups, monitoring, application resilience, and regular recovery testing.
Technical capabilities, supported hardware, licensing, distance limits, and configuration requirements can vary by Hitachi Vantara platform and software version. Organizations should consult the current official documentation and validate their specific architecture before deployment.
A. Global Active Device, or GAD, is a Hitachi Vantara storage technology that provides synchronous remote replication and active-active access between supported storage systems.
A. Its primary purpose is to improve data availability and storage resilience by maintaining synchronized copies of data across storage systems and supporting continued I/O during certain failure scenarios.
A. No. GAD is primarily a high-availability and replication technology. Independent backups remain important for recovering from corruption, accidental deletion, ransomware, and other logical data problems.
A. The quorum mechanism helps the storage systems determine which side should continue processing I/O during certain communication or system failures.
A. Yes. Hitachi documentation identifies virtual-machine migration without storage impact as one of the capabilities associated with GAD.
A. No. It is primarily relevant to organizations with workloads that justify the infrastructure, cost, and operational complexity of high-availability storage. Smaller or less critical environments may have simpler and more economical alternatives.