Getting started with Copy Services

This topic provides information about requirements and guidelines for using the point-in-time copy and remote mirror and copy features of Copy Services.

It is assumed that you have obtained the information that you need to activate the Copy Services licenses using the IBM Disk Storage Feature Activation (DSFA) Web site at: http://www.ibm.com/storage/dsfa/. After you obtain the activation keys, it is also assumed that you have entered them in the DS Storage Manager Web interface.

You can use the DS CLI or DS Storage Manager (GUI) to perform Copy Services tasks.

Note: For a listing of Copy Services commands, see the Command-line interface section of the DS6000 Information Center. For a listing of Copy Services tasks that you can perform from the DS Storage Manager, see the Managing section .

The following rules apply when using Copy Services functions:

One or more storage units must be assigned. Ensure that one or more storage units are configured, assigned, and operating in a normal state. See “Storage Units — Main Page” for more information. The number of required storage units depends on the function. For example, FlashCopy^® operations require one storage unit, but Metro Mirror and Global Mirror require two.
Note: If you plan to use Remote FlashCopy (known as Inband FlashCopy commands on the ESS 2105), two storage units are required for this configuration.
Physical connection must be established between two storage units. If you plan to use remote mirror and copy functions, such as Metro Mirror, Global Copy or Global Mirror), ensure that a physical connection is established between two storage units. Two (or more) storage units can be connected using a fibre channel direct connection or connect through a switch. To connect the storage units, it is recommended that you have one cable from c0 to c0 and one from c1 to c1, for example, and that you have the proper port topology configuration for those connections. To configure I/O ports, select, in the navigation, Real-time Manager > Storage units > Select Action: Configure I/O Ports... > Go.
Logical configuration must be created. Consider the following requirements:
1. Volume capacity: Ensure that the capacity of your target volumes is equal to or greater than your source volumes. When you select target volumes from the DS Storage Manager, it verifies that the capacities of the target volumes are at least as big as the source volumes. It does not allow you to select smaller-sized target volumes.
  Note: Be aware that for failover and failback operations to complete successfully, the volumes must be the same size and type.
2. Volume quantity: Ensure that you have at least one target volume for each source volume that is of equal or greater capacity than the source volume. You can create up to 256 volumes per LSS.
3. Volume sizes: Capacities of the volume are configured using the following conventions:
  Decimal
  
  1 GB (10 ⁹) = 1,000,000,000 bytes (ESS 2105 volumes are configured in decimal format.)
  
  Binary
  
  1 GB (2 ³⁰) = 1,073,741,824 bytes (DS volumes are configured in binary format.)
  This method provides volumes that fully use the capacity in every extent.
  
  Block
  
  1GB = (2 ³⁰) = 1,073,741,824 (iSeries™ volumes are configured in this format.)
  This method supports volume capacity in bytes (512-byte logical blocks). Supported storage sizes range from 1 to 4G blocks (the actual number of gigabytes is the number of blocks times 512).
  
  Note: You must consider the gigabyte definitions. In many applications, the source and target of a remote mirror and copy relationship must be exactly the same size. For example, if you plan to use DS6000 and ESS 2105 volumes for remote mirror and copy functions, the volumes on the DS6000 must be created in decimal format to be compatible with ESS volumes.
4. Logical subsystem: You can configure up to 32 LSSs. Each LSS is made up of either CKD or FB volumes. An LSS that consists of CKD addresses requires that other LSSs also be made up of CKD addresses. You can have both CKD and FB LSSs on the same storage unit.
  Note: CKD LSSs are referred to as LCUs in the DS Storage Manager.
Paths must be created: You must define paths for Metro Mirror, Global Copy, and Global Mirror functions. Fibre channel is used as the communications link between source and target volumes. To create paths, select, in the navigation, Real-time Manager > Copy Services > Paths. From the Select Action drop-down list, select Create... and then Go. See Creating remote mirror and copy paths for more information.
Relationships must be created: Determine which source and target volumes you wish to pair for Copy Services relationships. To create relationships, select, in the navigation, Real-time Manager > Copy Services > select the function (FlashCopy, Metro Mirror, or Global Mirror). From the Select Action drop-down list, select Create... and then Go. See Creating FlashCopy volume pairs or Creating Metro Mirror volume pairs, for example.

z/OS^® Global Mirror limitation:

If you plan to use z/OS Global Mirror (previously known as Extended Remote Copy or XRC), be aware that a z/OS Global Mirror environment that includes a DS8000 as a primary storage unit and a DS6000 as a secondary storage unit is not recommended for failover and failback operations because of the following limitations:

Performance mismatch (mirroring): If the secondary storage unit (the DS6000) and its connectivity to the System Data Mover (SDM) that runs on z/OS Global Mirror is significantly less capable (lower performing) than the primary storage unit and its connectivity to the application systems, the overall z/OS Global Mirror performance may suffer degraded performance. That is, if applications can write faster to primary storage units than the SDM can write to the secondary storage units, then implementation problems will result. (The SDM is the function that copies data from the primary storage unit to the secondary storage unit in a z/OS Global Mirror environment.)
Performance mismatch (running applications): Suppose a disaster or failure occurs and applications failover to the secondary (or recovery) site and are running using the secondary storage units. If the secondary storage unit (the DS6000) is less capable (performance-wise) than the primary storage unit, it is likely that you will not be able to complete primary business applications in the required or expected time frame.
z/OS Global Mirror-capable local (or primary) storage units: Suppose a disaster or failure occurs in an z/OS Global Mirror environment and applications failover to the secondary site and are running at the secondary site on the secondary storage units. Later, after the primary site has been repaired and is ready to resume as the primary site, the secondary storage unit can then use z/OS Global Mirror to failback to the primary site. However, for the failover and failback operations to work successfully, the secondary storage unit must be a z/OS Global Mirror-capable primary storage unit, which means it must be capable of being an z/OS Global Mirror primary storage unit. The DS6000 does not have the appropriate microcode functionality to be a z/OS Global Mirror-capable primary storage unit, and therefore cannot be used to failback to the primary site.

General considerations include:

If you plan to issue DS6000 commands, you must have the DS CLI prompt and be connected to a storage unit that will be used for open systems or zSeries^® host system storage. The DS CLI helps enable open systems hosts to invoke and manage FlashCopy and remote mirror and copy operations through batch processes and scripts. For more information, see the IBM^® System Storage™ DS6000 Command-Line Interface Guide.
Note: For more complex Copy Services environments, you might find invoking and managing Copy Services functions with the DS CLI is easier. With the DS CLI, you can save commands as scripts, which significantly reduces the time to create, edit, and verify their content.
When you issue a FlashCopy command with the Initiate background copy option enabled, the FlashCopy relationship is established, but put in a queue for background copying. The time that the background copying starts for the specific relationship depends on the number of FlashCopy volumes that have begun background copying or are waiting to begin. When the copy starts, the status displays as "background copy running" for that FlashCopy volume pair.
How long the actual physical copy takes can depend on the amount of data being copied and other activity that is occurring on the storage unit. for information on monitoring when the copy completes, see Viewing information about FlashCopy relationships.
You should be aware of some FlashCopy data consistency considerations. For example, there are environments where data is stored in server memory cache and written to disk at some later time. Buffers for a database management subsystem (DBMS) or metadata for a journaled file system are two examples of these environments. If a FlashCopy operation copies a source volume to a target volume, but buffers from the DBMS or metadata from the journaled file system are not flushed first, you might have to perform an incremental update. For a DBMS, you might have to back out of current transactions. For a journaled file system, you might have to run the fsck utility on the target volume.
To avoid these types of restart actions, ensure that all data that is related to the FlashCopy source volume has been written to disk before you perform the FlashCopy operation. For a DBMS, you can quiesce the subsystem or use a DBMS command such as DB2’s LOG SUSPEND. For a journaled file system, you can unmount the source volume before you perform a FlashCopy operation.
For FlashCopy operations: If you are going to automate your FlashCopy procedures, consider verifying the data consistency on your target volumes frequently. On some systems, such as AIX^®, Windows^®, and Linux^®, before performing FlashCopy operations, you must quiesce your applications that access FlashCopy source volumes. The source volumes must then be unmounted during the FlashCopy establishment. This is to ensure that there is no data in the buffers that could be flushed to the target volumes and potentially corrupt them.
You can use Global Mirror to create consistent copies of your data at a secondary site, with minimal impact to the local (or primary) site. Global Mirror uses the concept of sessions to internally manage data consistency across storage units. You can also use Metro Mirror, Global Copy, and FlashCopy (without Global Mirror) to create data consistency. However, this requires that you use either external automated software or manually suspend your applications at the local site to create consistency at your recovery (or secondary) site.
The DS Storage Manager can be used for almost all functions for Copy Services. However, you cannot issue the following functions from the DS Storage Manager. They are available only through the DS CLI:
FlashCopy consistency groups

Consistency group commands allow the storage unit to freeze I/O activity to a LUN or volume until you issue the FlashCopy consistency group command. Consistency groups help create a consistent point-in-time copy across multiple LUNs or volumes, and even across multiple storage units.

Remote FlashCopy (known as Inband FlashCopy commands on the ESS 2105)

Remote FlashCopy commands are issued to a source volume of a remote mirror and copy volume pair on a local storage unit and sent across paths (acting as a conduit) to a remote storage unit to enable a FlashCopy pair to be established at the remote site. This eliminates the need for a network connection to the remote site solely for the management of FlashCopy.
If you perform scenarios that call for freeze and run operations for remote mirror and copy operations, you must issue these requests from the command line interface, together with external automated software. These requests are not supported by the DS Storage Manager. (Automation software is not provided with the storage unit; it must be supplied by the user. However, IBM has offerings to assist with this automation. For more information, contact your IBM storage representative.)