DS8000 Copy Services overview
This chapter provides an overview of the Copy Services functions that are available with the DS8000 series models, including Remote Mirror and Copy, and Point-in-Time Copy functions.
These functions make the DS8000 series a key component for disaster recovery solutions, data migration activities, and for data duplication and backup solutions.
This chapter covers the following topics:
5.1 Introduction to Copy Services
Copy Services is a collection of functions that provide disaster recovery, data migration, and data duplication functions. With the Copy Services functions, for example, you can create backup data with little or no disruption to your application. You also can back up your application data to the remote site for disaster recovery.
The Copy Services functions run on the DS8880 storage unit and support open systems and z Systems environments. They are also supported on other DS8000 family models.
5.1.1 DS8000 Copy Services functions
Copy Services in the DS8000 include the following optional licensed functions:
•IBM System Storage FlashCopy, a point-in-time copy function
The FlashCopy Space Efficient function is not supported on the DS8880. Instead, you can define your FlashCopy targets as Extent Space Efficient volumes in an extent pool by using small extents.
•Remote mirror and copy functions:
– IBM System Storage Metro Mirror.
– IBM System Storage Global Copy.
– IBM System Storage Global Mirror.
– IBM System Storage Metro/Global Mirror, which is a three-site solution to meet the most rigorous business resiliency needs.
– IBM System Storage Multiple Target Peer-to-Peer Remote Copy (PPRC), which is another three-site solution that concurrently replicates a primary volume to two secondary volumes. It can be implemented as either two Metro Mirror relationships off the same primary volume or one Metro Mirror relationship and an asynchronous replication from the same primary volume concurrently.
•For IBM z Systems users, the following options are available:
– z/OS Global Mirror, which was known as Extended Remote Copy (XRC).
– z/OS Metro/Global Mirror, which is a three-site solution that combines z/OS Global Mirror and Metro Mirror.
Many design characteristics of the DS8000, its data copy and mirror capabilities, and features contribute to the full-time protection of your data.
The information that is provided in this chapter is only an overview. Copy Services are covered in more detail in the following materials:
•IBM DS8870 Copy Services for Open Systems, SG24-6788
•IBM DS8870 Copy Services for IBM z Systems, SG24-6787
•IBM DS8870 Multiple Target Peer-to-Peer Remote Copy, REDP-5151
5.1.2 Copy Services management interfaces
You control and manage the DS8000 Copy Services functions by using the following interfaces:
•Data storage command-line interface (DS CLI), which provides a set command that covers all Copy Services functions and options
•IBM Copy Services Manager (CSM), formerly known as Tivoli Storage Productivity Center for Replication, to manage large Copy Services implementations easily and to provide data consistency across multiple systems. With DS8000 Release 8.1 and later, CSM is preinstalled on the Hardware Management Console (HMC).
•DS Storage Manager, the graphical user interface (GUI) of the DS8000 (DS GUI)
•DS Open application programming interface (DS Open API)
z Systems users can also use the following interfaces:
•Time Sharing Option (TSO) commands
•Device Support Facilities (ICKDSF) utility commands
•ANTRQST application programming interface (API)
•Data Facility Storage Management Subsystem data set services (DFSMSdss) utility
5.2 FlashCopy
FlashCopy creates a point-in-time copy of the data. For open systems, FlashCopy creates a copy of the logical unit number (LUN). The target LUN must exist before you can use FlashCopy to copy the data from the source LUN to the target LUN.
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Note: FlashCopy Space Efficient (Track Space Efficient) is not supported by the DS8800. Instead, you can define your FlashCopy targets as Extent Space Efficient (ESE) volumes in an extent pool using small extents.
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When a FlashCopy operation is started, it takes less than a second to establish the FlashCopy relationship, which consists of the source and target volume pairing and the necessary control bitmaps. Thereafter, a copy of the source volume is available as though all the data was copied. When the pair is established, you can read and write to the source and target volumes.
The basic concepts of FlashCopy are explained in the following section and are shown in Figure 5-1.
Figure 5-1 FlashCopy concepts
If you access the source or the target volumes while the FlashCopy relationship exists, I/O requests are handled in the following manner:
•Read from the source volume
When a read request goes to the source, data is directly read from there.
•Read from the target volume
When a read request goes to the target volume, FlashCopy checks the bitmap and takes one of the following actions:
– If the requested data has been copied to the target, it is read from there.
– If the requested data has not yet been copied, it is read from the source.
•Write to the source volume
When a write request goes to the source, the data is first written to the cache and persistent memory (write cache). Later, when the data is destaged to the physical extents of the source volume, FlashCopy checks the bitmap for the location that is to be overwritten and takes one of the following actions:
– If the point-in-time data was already copied to the target, the update is written to the source directly.
– If the point-in-time data was not yet copied to the target, it is now copied immediately and only then is the update written to the source.
•Write to the target volume
Whenever data is written to the target volume while the FlashCopy relationship exists, the storage system checks the bitmap and updates it, if necessary. FlashCopy does not overwrite data that was written to the target with point-in-time data.
5.2.1 The FlashCopy background copy
By default, standard FlashCopy (also called FULL copy) starts a background copy process that copies all point-in-time data to the target volume. After the completion of this process, the FlashCopy relationship ends and the target volume becomes independent of the source.
The background copy can slightly affect application performance because the physical copy needs storage resources. The impact is minimal because host I/O always has higher priority than the background copy.
5.2.2 No background copy option
A standard FlashCopy relationship can also be established by using the NOCOPY option. With this option, FlashCopy does not start a background copy. Point-in-time data is copied only when a copy is required due to an update to the source or target. This option eliminates the impact of the background copy.
The NOCOPY option is useful in the following situations:
•When the target is not needed as an independent volume
•When repeated FlashCopy operations to the same target are expected
5.2.3 Benefits and use
The point-in-time copy that is created by FlashCopy often is used when you need to produce a copy of the production data with little or no application downtime. Use cases for the point-in-time copy that is created by FlashCopy include online backup, testing new applications, or creating a copy of transactional data for data mining purposes. To the host or application, the target looks exactly like the original source. It is an instantly available binary copy.
5.2.4 FlashCopy options
FlashCopy provides many more options and functions. These options and capabilities are described in this section:
Persistent FlashCopy
Persistent FlashCopy allows the FlashCopy relationship to remain even after the (FULL) copy operation completes. You must explicitly delete the relationship to end it.
Incremental FlashCopy (refresh target volume)
Incremental FlashCopy requires that the background copy and the Persistent FlashCopy options are enabled. The first full copy must be complete.
Refresh target volume refreshes a FlashCopy relationship without copying all data from the source to the target again. When a subsequent FlashCopy operation is initiated, only the changed tracks must be copied from the source to the target. The direction of the refresh also can be reversed from the (former) target to the source.
In many cases, only a small percentage of the entire data is changed in a day. In this situation, you can use this function for daily backups and save the time that is required for the physical copy of FlashCopy.
Multiple relationship FlashCopy
FlashCopy allows a source to have relationships with up to 12 targets simultaneously. A usage case for this feature is the creation of regular point-in-time copies as online backups or time stamps.
With DS8000 Licensed Internal Code (LIC) 7.7.40.xx, FlashCopy was enhanced to allow all FlashCopy source relationships to be incremental by introducing type 2 incremental FlashCopy relationships.
Two potential uses for multiple incremental FlashCopy relationships are shown:
•Database backup
When more than one backup is made with FlashCopy each day, they can all be incremental copies.
•Global Mirror test copy
The Global Mirror journal FlashCopy is an incremental copy. Multiple incremental copies now allow the test copy to also be incremental.
Data Set FlashCopy
By using Data Set FlashCopy, you can create a point-in-time copy of individual data sets instead of complete volumes in an IBM z Systems environment.
Consistency Group FlashCopy
By using Consistency Group FlashCopy, you can freeze and temporarily queue I/O activity to a volume. Consistency Group FlashCopy helps you to create a consistent point-in-time copy without quiescing the application across multiple volumes, and even across multiple storage units.
Consistency Group FlashCopy ensures that the order of dependent writes is always maintained. Therefore, Consistency Group FlashCopy creates host-consistent copies, not application-consistent copies. The copies have power-fail or crash-level consistency. To recover an application from Consistency Group FlashCopy target volumes, you must perform the same recovery as after a system crash or power outage.
FlashCopy on existing Metro Mirror or Global Copy primary
By using this option, you establish a FlashCopy relationship where the target is a Metro Mirror or Global Copy primary volume. Through this relationship, you create full or incremental point-in-time copies at a local site and then use remote mirroring to copy the data to the remote site.
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Important: You cannot perform a FlashCopy from a source to a target if the target also is a Global Mirror primary volume.
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For more information about Metro Mirror and Global Copy, see 5.3.1, “Metro Mirror” on page 131, and 5.3.2, “Global Copy” on page 132.
Inband commands over remote mirror link
In a remote mirror environment, commands to manage FlashCopy at the remote site can be issued from the local or intermediate site and transmitted over the remote mirror Fibre Channel links. This ability eliminates the need for a network connection to the remote site solely for the management of FlashCopy.
5.2.5 Remote Pair FlashCopy (Preserve Mirror)
Remote Pair FlashCopy (also referred to as Preserve Mirror) transmits the FlashCopy command to the remote site if the target volume is mirrored with Metro Mirror. As the name implies, Preserve Mirror preserves the existing Metro Mirror status of FULL DUPLEX.
For more information about Remote Pair FlashCopy, see IBM System Storage DS8000: Remote Pair FlashCopy (Preserve Mirror), REDP-4504.
5.2.6 Remote Pair FlashCopy with Multiple Target PPRC
Multiple Target PPRC allows a single Metro Mirror, Global Mirror, or Global Copy primary to have two secondary volumes. Additional considerations are involved to use Remote Pair FlashCopy in a Multiple Target PPRC environment. For more information, see IBM DS8870 Multiple Target Peer-to-Peer Remote Copy, REDP-5151.
5.3 Remote Mirror and Copy
The Remote Mirror and Copy functions of the DS8000 are a set of flexible data mirroring solutions that allow replication between volumes on two or more disk storage systems. These functions are used to implement remote data backup and disaster recovery solutions.
The following Remote Mirror and Copy functions are optional licensed functions of the DS8000:
Remote Mirror functions can be used in open systems and z Systems environments.
In addition, z Systems users can use the DS8000 for the following functions:
•IBM Geographically Dispersed Parallel Sysplex (IBM GDPS)
5.3.1 Metro Mirror
Metro Mirror provides real-time mirroring of logical volumes between two DS8880s, or any other combination of DS8870, DS8100, DS8300, DS8700, DS8800, DS6800, and ESS800. These volumes can be located up to 300 km (186.4 miles) from each other. It is a synchronous copy solution in which a write operation must be carried out on both copies, at the local and remote sites, before it is considered complete.
The basic operational characteristics of Metro Mirror are shown in Figure 5-2.
Figure 5-2 Metro Mirror basic operation
5.3.2 Global Copy
Global Copy copies data asynchronously and over longer distances than is possible with Metro Mirror. Global Copy is included in the Metro Mirror or Global Mirror license. When you are operating in Global Copy mode, the source does not wait for copy completion on the target before a host write operation is acknowledged. Therefore, the host is not affected by the Global Copy operation. Write data is sent to the target because the connecting network allows an independent of the order of the host writes. This configuration makes the target data lag behind and is inconsistent during normal operation.
You must take extra steps to make Global Copy target data usable at specific points in time. The steps that are used depend on the purpose of the copy:
•Data migration
You can use Global Copy to migrate data over long distances. When you want to switch from old to new data, you must stop the applications on the old site, tell Global Copy to synchronize the data, and wait until it is finished.
•Asynchronous mirroring
Global Copy is also used to create a full-copy of data from an existing system to a new system without affecting client performance. If the Global Copy is incomplete, the data at the remote system is not consistent. When the Global Copy completes, you can stop it and then start with the Copy relationship (Metro Mirror or Global Mirror) starting with a full resynchronization so the data is consistent.
5.3.3 Global Mirror
Global Mirror is a two-site, long distance, asynchronous, remote copy technology. This solution integrates the Global Copy and FlashCopy technologies. With Global Mirror, the data that the host writes at the local site is asynchronously mirrored to the storage unit at the remote site. With special management steps (under control of the local master storage unit), a consistent copy of the data is automatically maintained and periodically updated by using FlashCopy on the storage unit at the remote site.
You need extra storage at the remote site for these FlashCopies. However, starting with DS8880 Release 8.1, you can define your FlashCopy targets as Extent Space Efficient ESE volumes in an extent pool using small extents.
Global Mirror features the following benefits:
•Support for almost unlimited distances between the local and remote sites, with the distance typically limited only by the capabilities of the network and the channel extension technology. You can use this unlimited distance to choose your remote site location based on business needs. This capability enables site separation to add protection from globalized disasters.
•A consistent and restartable copy of the data at the remote site, which is created with minimal impact to applications at the local site.
•Data currency where, for many environments, the remote site lags behind the local site typically 3 - 5 seconds, which minimizes the amount of data exposure if an unplanned outage occurs. The actual lag in data currency that you experience depends on many factors, including specific workload characteristics and bandwidth between the local and remote sites.
•Dynamic selection of the recovery point objective (RPO) that you want, based on business requirements and optimization of available bandwidth.
•Session support in which data consistency at the remote site is internally managed across up to eight storage units that are at the local site and the remote site.
•Efficient synchronization of the local and remote sites with support for failover and failback operations. This configuration helps to reduce the time that is required to switch back to the local site after a planned or unplanned outage.
The basic operational characteristics of Global Mirror are shown in Figure 5-3.
Figure 5-3 Global Mirror basic operation
The H1 volumes at the local site are the production volumes. They are used as Global Copy primaries. The data from the H1 volumes is replicated to the H2 volumes by using Global Copy. At a certain point, a consistency group is created from all of the H1 volumes, even if they are in separate storage units. This creation has little impact on applications because the creation of the consistency group is quick (often a few milliseconds).
After the consistency group is created, the application writes can continue updating the H1 volumes. The missing increment of the consistent data is sent to the H2 volumes by using the existing Global Copy relationships. After all data reaches the H2 volumes, Global Copy is halted for a brief period while Global Mirror creates a FlashCopy from the H2 to the J2 volumes. These volumes now contain a consistent set of data at the secondary site.
The data at the remote site typically is current within 3 - 5 seconds, but this recovery point depends on the workload and bandwidth that is available to the remote site.
With its efficient and autonomic implementation, Global Mirror is a solution for disaster recovery implementations where a consistent copy of the data must always be available at a remote location that is separated by a long distance from the production site.
5.3.4 Metro/Global Mirror
Metro/Global Mirror is a three-site, multi-purpose, replication solution. Metro Mirror from local site H1 to intermediate site H2 provides high availability replication. Global Mirror from intermediate site H2 to remote site H3 provides long-distance disaster recovery replication with Global Mirror (Figure 5-4). This cascaded approach for a three-site solution does not burden the primary storage system with sending out the data twice.
Figure 5-4 Cascaded Metro/Global Mirror elements
Metro Mirror and Global Mirror are well-established replication solutions. Metro/Global Mirror combines Metro Mirror and Global Mirror to incorporate the following best features of the two solutions:
•Metro Mirror:
– Synchronous operation supports zero data loss.
– The opportunity to locate the intermediate site disk systems close to the local site allows the use of intermediate site disk systems in a high-availability configuration.
•Global Mirror:
– Asynchronous operation supports long-distance replication for disaster recovery.
– The Global Mirror methodology has no effect on applications at the local site.
– This solution provides a recoverable, restartable, and consistent image at the remote site with an RPO, typically within 3 - 5 seconds.
Multiple Global Mirror sessions
The DS8870 supports several Global Mirror (GM) sessions within a storage system (storage facility image (SFI)). Up to 32 Global Mirror hardware sessions can be supported within the same DS8870. The basic management of a GM session does not change. The GM session builds on the existing Global Mirror technology and LIC of the DS8000.
For details, see the “Global Mirror Overview” chapter in IBM DS8870 Copy Services for IBM z Systems, SG24-6787, or IBM DS8870 Copy Services for Open Systems, SG24-6788.
GM and MGM collision avoidance
Global Copy and GM are asynchronous functions that are suited for long distances between a primary and a secondary DS8000 storage system. At a long distance, it is important to allow hosts to complete an I/O operation, even if the transaction on the remote site is incomplete.
During high activity (for example, long-running batch jobs), multiple writes might update the same track or block, which can result in a collision. To avoid such collisions, Global Mirror locks tracks in the consistency group (CG) on the primary DS8000 at the end of the CG formation window.
5.3.5 Multi-Target PPRC
IBM Multi-Target PPRC enhances a multi-site disaster recovery environment by providing the capability to have two PPRC relationships on a single primary volume, allowing use of another remote site for extra data protection.
Multi-Target PPRC provides the following enhancements:
•Mirrors data from a single primary (local) site to two secondary (remote) sites
•Provides an increased capability and flexibility in the following disaster recovery solutions:
– Synchronous replication
– Asynchronous replication
– Combination of synchronous replication and asynchronous replication configurations
•Improves a cascaded Metro/Global Mirror configuration and simplifies certain procedures
Before Multi-Target PPRC, it was possible for a primary volume to mirror data to only one secondary volume. With Multi-Target PPRC, the same primary volume can have more than one target, allowing data to be mirrored from a single primary site to two target sites.
Figure 5-5 shows a general Multi-Target PPRC topology where a single primary site is replicated to two secondary sites. Host I/O is directed to the H1 site and Multi-Target PPRC mirrors the updates to both H2 and H3.
Figure 5-5 Basic Multi-Target PPRC configuration
A primary volume can have any combination of two Metro Mirror, Global Copy, or Global Mirror relationships, with a restriction that a primary volume can belong to only one Global Mirror session at a time.
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Note: A volume can be in only one Global Mirror session.
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Little extra host response time impact occurs with two relationships compared to one relationship of the same type. Multi-Target PPRC is available in both open systems and z Systems environments.
For more information, see IBM DS8870 Multiple Target Peer-to-Peer Remote Copy, REDP-5151.
5.3.6 z/OS Global Mirror
z/OS Global Mirror, which was known as Extended Remote Copy (XRC), is a copy function that is available for the z/OS operating system. The basic operational characteristics of z/OS Global Mirror are shown in Figure 5-6.
Figure 5-6 z/OS Global Mirror basic operations
It involves the System Data Mover (SDM), which is part of DFSMSdfp. DFSMSdfp in turn is a part of z/OS. z/OS Global Mirror maintains a consistent copy of the data asynchronously at a remote location. It can be implemented over unlimited distances. It is a combined hardware and software solution that offers data integrity and data availability that can be used as part of business continuance solutions, for workload movement, and for data migration.
The z/OS Global Mirror function is an optional licensed function (called Remote Mirroring for z Systems (RMZ)) of the DS8000 that enables the SDM to communicate with the primary DS8000. No z/OS Global Mirror license is required for the storage system in site H2. It can be any storage system that is supported by z/OS. However, consider that you might want to reverse the mirror, in which case, your auxiliary storage system needs a z/OS Global Mirror license as well.
5.3.7 z/OS Metro/Global Mirror
This mirroring configuration uses Metro Mirror to replicate primary site data to a location within the metropolitan area. It also uses z/OS Global Mirror to replicate primary site data to a location that is a long distance away. This configuration enables a z/OS three-site high-availability and disaster recovery solution for even greater protection against unplanned outages.
The basic operational characteristics of a z/OS Metro/Global Mirror implementation are shown in Figure 5-7.
Figure 5-7 z/OS Metro/Global Mirror
5.3.8 GDPS on z/OS environments
GDPS is the IBM solution for managing large and complex environments and to keep the client data safe and consistent. It provides an easy interface to manage multiple sites with MGM pairs.
With its HyperSwap capability, GDPS is the ideal solution if you want 99.9999% availability.
GDPS easily monitors and manages your MGM pairs, and it also allows clients to run disaster recovery tests without affecting production. These features lead to faster recovery from real disaster events.
GDPS functions include the following examples:
•The option to hot swap between primary and secondary Metro Mirror is managed concurrently with client operations. Operations can continue if a disaster or planned outage occurs.
•Disaster recovery management in a disaster at the primary site allows operations to restart at the remote site quickly and safely while data consistency is continuously monitored.
•GDPS freezes the Metro Mirror pairs if a problem with mirroring occurs. It restarts the copy process to secondaries after the problem is evaluated and solved, maintaining data consistency on all pairs.
For more information about GDPS, see IBM GDPS Family: An Introduction to Concepts and Capabilities, SG24-6374.
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