Using FlashCopy Version 2 for DB2 UDB for OS/390 & z/OS Object-Level Migration

by Daniel L. Luksetich
August 1, 2004

FlashCopy is an IBM microcode-based technology that comes as an add-on feature to the more advanced IBM DASD subsystems. Other DASD manufacturers typically have similar capabilities under different names. This technology lets the DASD subsystem handle some of the data movement task rather than relying on the operating system or programs. FlashCopy is a useful utility for backing up databases and moving large volumes of data quickly at a DASD volume level. FlashCopy Version 2 introduces data set level copy.

FlashCopy V2 is available for some of the IBM storage subsystems and may already be available now or will soon be available for HDS and EMC subsystems. This article will focus on a technique for using this technology to move  DB2 objects between databases and subsystems much faster than traditional techniques. Use of this technology will change the way we move our data!

Migrating DB2 Data

DBAs are moving data continuously to:

• Copy data from production to test
• Archive data
• Snap a copy of the data for separate analysis
• Clone a database.

 

A DBA can employ several techniques to move DB2 data from one object to another. Among the safest options is an unload/load. Using the DSN1COPY stand-alone utility is more risky. Other utilities can be used for data migration; these include DFDSS, AMS REPRO, and FDR (see the DB2 Administration Guide for the complete list).

The DBA begins the process by creating target tablespaces, tables, and indexes that match the source object entirely. The target objects can be in the same or different databases, or even in a different DB2 subsystem.

If unload/load is the method chosen, then the DSNTIAUL or equivalent program is used to unload the source tablespace data into flat files. The DB2 LOAD online utility (or equivalent third-party LOAD utility) is then used at the target to populate the tablespace and build the indexes. This is the safest method, since it’s in DB2’s control. This method also allows the source tablespaces to be online during the unload process.

If DSN1COPY is chosen, the source tablespace and indexspaces can be copied directly from the source to the target. This is significantly faster than the unload/load method, since the data doesn’t have to be staged in a flat file. Also, indexes can be copied using this technique, which can improve speed. The DBA is responsible for translation of internal DB2 object identifiers. Since DSN1COPY is an offline utility, it requires control of the underlying data sets at the source and target. That means DB2 objects affected must be offline for this process to work. It’s a trade-off between speed and availability.

FlashCopy V2 offers a technique similar to DSN1COPY. However, this technology will dramatically reduce the CPU and elapsed time required to move the data. Using the dfsmsDSS system utility, FlashCopy V2 can be used to quickly copy the data from source to target, and reduce the outages associated with DSN1COPY.