Provide “True” Enterprise-Class Data Protection for Your Apps The Advantages of Hitachi Global-Active Device

By Hubert Yoshida posted 12-11-2018 00:00



The days when data recovery solutions were evaluated on how they could minimize the two R’s are over. The two R’s stand for Recovery Point Objective, RPO, how much new or changed data is lost because it hasn’t been backup yet, and Recovery Time Objective, RTO, how long it takes to resume operations. The reason I say this is because we can achieve zero RPO and zero RTO with today’s Global-Active Device on our family of Hybrid G Series and All Flash F Series Virtual Storage Platform, VSP, storage arrays.

The Global-Active Device (GAD) is another virtualization capability of the VSP storage platform that creates a virtual storage machine. A virtual storage machine virtualizes two separate VSP storage arrays and makes them appear as one storage array to a host server or a cluster of host servers. GAD is configured so that the primary and secondary storage systems use the actual information of the primary storage system, and the global-active device primary and secondary volumes are assigned the same virtual LDEV number in the virtual storage machine. This enables the host to see the pair volumes as a single volume on a single storage system, and both volumes receive the same data from the host. When a write is done to one of the GAD pair volumes, the data is replicated to the other pair and acknowledged before a write complete is returned to the initiator of the write. That keeps the volumes in synch and ensures zero RPO and zero RTO in the event of a storage system or site failure.

The virtual storage machine can span across physical storage systems that are separated by up to metro distances (500 kilometers). GAD provides non-disruptive, high availability (HA), disaster recovery (DR), and rapid data center migration services. In addition, it enables painless virtual machine storage motion where the location of the storage underlying virtual machines is moved between storage environments for load balancing or maintenance. GAD supports active-active processing of shared data, meaning that all interfaces to the storage system are always active, and the system synchronizes writes across the entire storage system. GAD can be configured in a single or clustered server configuration.


Some vendors might use their synchronous replication product to create a synchronized copy pair. This creates an Active/Passive pair on separate storage arrays. Processing occurs on the primary side of the pair and the passive side is only used for fail-over. This does not provide active-active processing of shared data. In order to achieve active-active processing, GAD provides three key features that distinguishes it from synchronous replication products.

  1. The first is a streamlined locking mechanism between the storage systems to synchronize the writes.
  2. The second is preservation of SCSI reserves, a control mechanism for avoiding conflicts or congestion with different host initiators.
  3. The third is a quorum disk to resolve conflicts between the active-active pair of storage systems.

The quorum disk is an external storage system that acts as a heartbeat for the GAD pair, with both storage systems accessing the quorum disk to check on each other. A communication failure between systems results in a series of checks with the quorum disk to identify the problem for the system to be able to receive host updates. The external quorum disk is accessed like a virtualized external disk which means that it can be a third party disk. It can also be on a virtual or physical server that has software to present itself as a disk. The quorum disk can also be in the cloud through the use of iSCSI. However, if GAD is used simply for non-disruptive migration, no quorum disk is needed.

GAD is a copy technology and can be one of multiple overlapping data copy technologies that are used in a production system. Backup and point in time copies are still required to protect against data corruption caused by errors or malicious attacks. While GAD provides protection in a metro area, an asynchronous, out of region replication with Hitachi Universal Replicator (HUR) might also be required in addition to GAD. Copy technologies include synchronous and asynchronous copies, clones, snap shots, and thin images or virtual copies. Copies are not only used for operational and disaster recovery, but also for archive, big data, analytics, audits, e-discovery, development and test, and other data repurposing requirements. IDC estimates that 60% 0f corporate data consists of copies of original data, and that on average, organizations have 13 copies of each data object. Managing the life cycle of copies is a major challenge. Unmanaged or orphan copies of data can be a liability. Hitachi Vantara’s Hitachi Data Instance Director provides a copy data management platform that simplifies creating and managing policy-based workflows that support business functions with controlled copies of data. Integration with Hitachi Data Instance Director is a key advantage of Hitachi Vantara’s GAD.


Hitachi’s Global Active Device is the leader in active-active, continuous availability. Other storage vendors may claim similar replication capabilities. Since they all rely on synchronous replication over metro distances there is not much difference in performance. However, there is a great deal of difference in simplicity, scalability, and ROI.

  • Simplicity. Hitachi’s implementation is simple in that it is an extension of the virtualization capability of our Storage Virtualization Operating System RF (SVOS RF). There are no additional appliances required to virtualize the pair of devices or additional software required in the host servers or virtual machines. No BIN files are required to set the configuration. Our virtualization also provides the most choices for selection of a quorum device. Integration with Hitachi Data Instance Director makes it easy to manage the interactions with other data copy technologies and application requirements.
  • Scalability. The way we have stream-lined the synchronous replication of the GAD pairs and preserved the SCSI reserves provides greater scalability than competitive implementations. Competitive solutions that require the use of appliances scale by adding more appliances and this also adds more complexity. Hitachi GAD provides true active-active processing of shared data, across the storage arrays. This scales beyond other implementations where only one storage array is active while the other is used for standby. The controllers in each VSP storage array are also active-active which gives us greater scalability than other vendor’s controllers that are Active/Passive or ALUA (Asymmetric Logical Unit Access). (see my previous blog on the differences in storage array controllers)
  • ROI. The return on your investment is higher with GAD due to our overall virtualization capability to virtualize external storage and create virtual storage machines. You can virtualize your existing storage behind a VSP array and create a virtual storage machine with another VSP over metro distances. Neither VSP in this scenario requires any capacity from a Hitachi storage system, all the capacity can be from virtualized 3rdparty storage systems. All VSP systems, from midrange to high-end enterprise support GAD, so you don’t need to have different solutions and different management tools for midrange, entry enterprise or high-end enterprise. No additional appliances or host software is required to support GAD. GAD also integrates well with other copy requirements such as HUR and thin images since it is a feature in SVSO RF. The use of Hitachi Instance director with GAD also reduces the cost of copy management and ensures that resources are not wasted on copies that are no longer needed.

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For more information on Hitachi Vantara’s GAD implementation