Providing for data backup has been part of I/T operations since its early days. Although today’s disk is much more stable that the disk devices 40 years ago and we rarely see “head crashes” any more, the need to provide back up data is still important. Reasons such as data migration, securing against logical data corruptions, protection from control unit failures, collecting accounting statistics, or providing for disaster recovery are still important. System z technology provides efficient backup and recovery capabilities through its copy services.
With the Copy Services functions, you can create backup data with little or no disruption to your application, and you can back up your application data to the remote site for disaster recovery.
Many design characteristics of the DS8000 and its data copying and mirroring capabilities contribute to the protection of your data, 24 hours a day and 7 days a week (24x7). The optional licensed functions of Copy Services are:
- FlashCopy creates a copy of a volume at a specific point-in-time, sometimes called a Point-in-Time copy, instantaneous copy, or time-zero copy. It takes only a few seconds to establish the FlashCopy relationships for tens to hundreds or more volume pairs. The copies are then immediately available for both read and write access. In a 24x7 environment, the quickness of the FlashCopy operation allows use in very large environments. Multiple FlashCopies of the same volume can be used with different applications.
FlashCopy is suitable for the following operational environments:
- Production backup system: A FlashCopy of the production data allows data recovery from an older level of data. This might be necessary due to a user error or a logical application error.
- Data backup system: A FlashCopy of the production data allows the client to create backups with the shortest possible application outage. The main reason for data backup is to provide protection in case of source data loss due to disaster, hardware failure, software failure, or user errors.
- Data mining system: A FlashCopy of the data can be used for data analysis, thus avoiding performance impacts for the production system due to long running data mining tasks.
- Test system: Test environments created by FlashCopy can be used by the development team to test new application functions with real production data — hence, a faster test setup process.
- Integration system: New application releases are likely to be tested prior to putting them onto a production server. By using FlashCopy, a copy of the production data can be established and used for integration tests.
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- Metro Mirror (previously known as synchronous Peer-to-Peer Remote Copy, or PPRC) provides real-time mirroring of logical volumes between two DS8000s that can be located up to 300 km from each other. It is a synchronous copy solution where write operations are completed on both copies (local and remote site) before they are considered to be complete. It is typically used for applications that cannot suffer any data loss in the event of a failure. As data is synchronously transferred, the distance between primary and secondary disk subsystems will determine the effect on application response time.
In order to restart applications at the remote site successfully, the remote site volumes must have consistent data. In normal operation, Metro Mirror keeps data consistency at the remote site. However, in case of a rolling disaster type of situation, the use of the Consistency Group option is used to keep data consistency at the remote site. An extended long busy (for z/OS) or queue full (for distributed systems) conditions are triggered when the control unit detects a condition where it cannot update the Metro Mirror secondary volume. The volume pair that first detects the error will go into the extended long busy condition, such that it will not do any writes. For z/OS, a system message will be issued (IEA494I state change message); for distributed systems, an SNMP trap message will be issued. These messages can be used as a trigger for automation purposes that will provide data consistency.
Metro Mirror allows several different options for improved availability:
- Freeze: Initiated by automated procedures, this is designed to freeze the image of the secondary data at the very first sign of a disaster, even before any database managers are made aware of I/O errors. This can prevent the logical contamination of the secondary copy of data that would occur if any storage subsystem mirroring were to continue after a failure that prevents some, but not all secondary volumes from being updated.
- HyperSwap: HyperSwap is designed to transparently switch to use secondary disk subsystems which contain mirrored data consistent with the primary data in seconds, without requiring applications to be quiesced. This allows near-continuous data availability in the event of a primary disk subsystem or site failure unplanned event, as well as the ability to perform disk maintenance and planned site maintenance for planned events. HyperSwap helps remove Disk subsystem failures as a single point of failure for an entire sysplex.
HyperSwap is available with GDPS/PPRC, GDPS/PPRC HyperSwap Manager, and z/OS R9 Basic HyperSwap function.
- Failover / Failback: For planned reconfigurations, FO/FB may reduce the overall elapsed time to switch the disk subsystems, thereby reducing the time that applications are unavailable to users. For unplanned reconfigurations, Failover/Failback allows the secondary disks to be configured in the suspended state after the switch and record any updates made to the data. When the failure condition has been repaired, resynchronizing back to the original primary disks requires only the changed data to be copied, thus eliminating the need to perform a full copy of the data. The window during which critical data is left without Metro Mirror protection following an unplanned reconfiguration is thereby minimized.
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- Global Mirror provides a long-distance remote copy feature across two sites using asynchronous technology. This solution is based on the existing Global Copy and FlashCopy. With Global Mirror, the data that the host writes to the storage unit at the local site is asynchronously shadowed to the storage unit at the remote site. A consistent copy of the data is automatically maintained on the storage unit at the remote site.
This efficient asynchronous mirroring technique allows the replication of data over long distances, without impacting the application I/O response time, its operation would be transparent and autonomic from the users point of view, and most importantly would provide a consistent copy of the data at the remote site at all times.
- At the local site, temporarily pause the application write I/Os on the primary A volumes.
- Wait for and make sure that the primary A volumes and the secondary B volumes become synchronized.
- Using FlashCopy, create a point-in-time (PiT) copy of the B volumes at the remote site.
- The FlashCopy targets, that is the C volumes, will then hold a copy of the A volumes at the time the application was paused or stopped. In this manner data consistency is kept at the remote site.
- Restart or resume the application write I/O activity to the A volumes.
Global Mirror operations provide the benefit of supporting operations over virtually unlimited distances between the local and remote sites. It can also provide a consistent and restartable copy of the data at the remote site, created with minimal impact to applications at the local site.
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z/OS Global Mirror
- z/OS Global Mirror is a copy function available for z/OS and Linux on System z operating systems. As with Global Mirror, z/OS Global Mirror can provide consistent data at virtually unlimited distances with negligible impact to application response times. By using the System Data Mover (SDM) component of z/OS, z/OS Global Mirror maintains a copy of the data asynchronously at a remote location, and can be implemented over virtually unlimited distances. It is a combined hardware and software solution that offers data consistency and data availability and can be used as part of business continuance solutions, for workload movement, and for data migration.
Starting on the IBM System z10 servers, the SDMs can be placed on zIIP engines for HW and SW savings. The z/OS Global Mirror function is an optional licensed function of the DS8000.
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- Metro Mirror provides near-continuous data availability with HyperSwap, and allows zero data loss. Global Mirror and z/OS Global Mirror provide protection from regional events with little to no impact to the end user. Combining the two in a “three-site” solution provides the best of both worlds, using Metro/Global Mirror in a cascading configuration, or Metro/z/OS Global Mirror in a multi-target configuration.