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AIX > Administrator > High Availability

HyperSwap Helps Keep Storage From Becoming a Single Point of Failure


Editor’s note: This is the first in a three-part series about PowerHA SystemMirror for AIX Enterprise Edition.

The availability of data centers and services is one of the most important topics of IT infrastructure, and each day, this topic draws more attention. Replication of data between sites is a good way to minimize business disruption since backup restores can take too long to meet business requirements, and depending on the extent of a disaster, equipment can be damaged and not available to restoring data. Recovery options vary in terms of cost, downtime and data loss.

Offering short recovery times and virtually no data loss, the PowerHA SystemMirror for AIX Enterprise Edition is a disaster recovery (DR) and high availability solution that helps automate node failures and application events to ensure availability. It helps automate recovery actions for storage failures on selected storage—controlling storage replication between sites (separate data centers) and enabling recoveries for entire site failures. It, therefore, ensures copies are in a consistent state to make the failover, enabling organizations to build a DR solution.

HyperSwap is one of the offerings from the PowerHA SystemMirror Enterprise Edition portfolio. This function provides for continuous availability against storage errors by using storage-based synchronous replication or peer-to-peer remote copy (PPRC). When directed, or upon a disk failure, an AIX host accessing the primary disk subsystem transparently switches to the backup copy of the data so users of the disks (such as middleware) aren’t affected.

HyperSwap Overview

Originally introduced in Geographically Dispersed Parallel Sysplex, HyperSwap is designed for the Metro Mirror (previously Synchronous PPRC) environment, where it enhances the resilience of Parallel Sysplex by facilitating the immediate switching of PPRC-mirrored disk subsystems.

HyperSwap technology enables the host to transparently switch an application’s I/O operations to secondary Metro Mirror volumes, provided physical connectivity exists between the host and the secondary storage subsystem. This affords the ability to provide continuous operations from a single site or from multiple locations within metro distances (up to 100 km). By implementing HyperSwap, disk failures, maintenance functions, etc., can be endured without interrupting application service.

This solution offers better DR solutions and demonstrates the close integration of PowerHA with IBM Storage as illustrated in Figure 1. HyperSwap technology enables PowerHA SystemMirror to support capabilities such as:

  • Eliminating primary disk subsystems as a single point of failure to provide the next level of continuous operations support within metro distances
  • Enabling storage maintenance without any application downtime
  • Migrating from old to new storage

All of these use cases fall into one of the two types of HyperSwap activity:

1. Unplanned HyperSwap. When primary storage fails, the OS that hosts the application detects and reacts to the event by performing a PPRC failover such that the application I/Os are transparently redirected to the secondary storage subsystem, thereby allowing the applications to continue running without interruption. In this case, errors are detected by the SCSI disk drivers in the OS, and the decision is made across multiple hosts to switch over to the secondary storage subsystem wholesale. For the duration of the HyperSwap swapping process, I/O is temporarily frozen from proceeding further. During this time, applications won’t experience failure but rather non-lethal delays.

2. Planned HyperSwap. In this scenario, an administrator initiates a HyperSwap from the primary to the secondary storage subsystem. Once the administrator requests the planned HyperSwap, I/O activity is frozen after coordination across the hosts in the cluster. The swap is performed, and then I/O operations are allowed to continue. Planned HyperSwap is helpful for performing maintenance on the primary storage and also for migrating from an old to a new storage subsystem.

Superior Storage Solution

HyperSwap support with PowerHA SystemMirror provides many benefits. This solution enables:

  • Continuous availability against storage failures
  • Secondary storage to automatically take the place of a failed primary device
  • Applications to continue running in a non-disruptive manner, as shown in Figure 2
  • The HyperSwap device configuration to be transparent to applications
  • Consistent group management across DS8K systems, as illustrated in Figure 3
  • Support for critical system disks, such as rootvg, paging and dump devices, and repository disks
  • Disk grouping
  • Cluster nodes to access instances of application disks that are being replicated
  • Support for multi-site deployments

For clients with a keen interest in storage availability and those who want to prevent storage from becoming a single point of failure—thereby avoid unnecessary cluster outages—PowerHA SystemMirror HyperSwap provides a good solution. With HyperSwap, DS8800 clients connect their storage servers with Metro Mirror, which continuously mirrors the storage between servers within a metro area (i.e. data center and DR sites) thereby ensuring almost no data loss. It also provides for planned maintenance of storage to be done without worrying about taking application downtime and thus disrupting services.

Kunal Langer is a technical solutions architect, Power Systems, AIX and PowerHA, with the Systems and Technology Group Lab-Based Services and Training.



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