IBM V7.2 manual Overview of Copy Services

Overview of Copy Services

Copy Services is a separately priced feature of the ESS, which provides powerful functions for replication of mission-critical data. For the Open Systems environment Copy Services offer point-in-time replication with FlashCopy and dynamic synchronous mirroring to a remote ESS with Peer-to-Peer Remote Copy (PPRC). The examples described in this paper use FlashCopy.

FlashCopy creates instant point-in-time copies of logical volumes (LVs) for purposes such as data backup or data duplication. The copy is called time-zero (T0) copy. It is a binary copy that looks exactly the same as the source volume at the time the copy was made.

When executing FlashCopy the ESS establishes the FlashCopy pairs and creates control bitmaps. This only takes a few seconds. Both source and target volumes can be accessed immediately after the FlashCopy pairs have been established, and the bitmaps created. Background tasks continue copying the data from the source to the target volumes. The FlashCopy relationship between source and target volume ends when the physical background copy tasks completed. Source and target volume can be accessed and modified independently.

FlashCopy can also be used with the ‘no copy’ option. This suppresses copying of the complete source volume. Only the data that changes on the source volume is copied to the target volume before the changes are made on the source volume. The FlashCopy relationship between source and target volume exists until it is withdrawn manually. When the FlashCopy relationship ends, the copy is no longer available for use.

Here are the restrictions for FlashCopy:

•A FlashCopy relationship can only be established between disk volumes. Source and target volumes have to reside within the same Open System’s Logical Subsystem (LSS).

•The target disk must have the same size as the source volume or must be bigger.

•Both source and target volumes can only be involved in one FlashCopy relationship at a time

•The target can only be used on the same operating system.

Copy Services run inside the ESS. FlashCopy can be used to quickly create copies of production data for the purpose of taking backups, creating test systems, or creating database copies for data mining purposes or data warehouses. FlashCopy has no significant impact on the performance nor does it require downtime of the production system.

Using PPRC, one ESS has to be defined as the Primary Copy Services Server. This ESS holds all Copy Services related information (i.e. the volumes and their current state). Optionally a second ESS could be defined to be the Backup Copy Services Server. On each ESS that is intended to use Copy Services there is a Copy Services client running which communicates with the server. Access to Copy Services is provided through an Internet browser. This allows for controlling the ESS copy functionality over the network from any platform for which the browser is supported.

Overview of FlashCopy 5