IBM DS8000 manual Basic copy commands, Copy raw devices

Reasons against using these methods could include:

￿Different methods are necessary for different data types and operating systems

￿Strong involvement of the system administrator is necessary

Today the majority of data migration tasks are performed with one of the methods discussed in the following sections.

Basic copy commands

Using copy commands is the simplest way to move data from one storage system to another, for example:

￿copy, xcopy, drag and drop for Windows

￿cp, cpio for UNIX

These commands are available on every system supported for DS8000 attachment, but work only with data organized in file systems. Data can be copied between file systems of different sizes. Therefore this method can be used for the consolidation of small volumes into larger ones. Figure 16-2outlines the process.

Host

Host

Stop applications

Copy all data

Restart

using new copy

Figure 16-2 Migration with copy commands

The most significant disadvantage of this method is the disruptiveness. To preserve data consistency, the applications writing to the data which is migrated have to be interrupted for the duration of the copy process. Furthermore, some copy commands cannot preserve advanced metadata, such as access control lists or permissions.

Attention: If your storage systems are attached through multiple paths, make sure that the multipath drivers for the old and the new storage system can coexist on one host. If not, you have to revert the host to a single path configuration before you attach the new storage system. You can change back to a multipath configuration after the migration is complete.

This is valid for all migration methods where source and target are attached to the host at the same time.

Copy raw devices

For raw data there are tools that allow you to read and write disk devices directly, such as dd for UNIX. They copy the data and its organizational structure (metadata) without having any intelligence about it. Therefore they cannot be used for consolidation of small volumes into larger ones. Special care has to be taken when data and its metadata are kept in separate places. They both have to be copied and realigned on the target system. By themselves, they are useless.

336DS8000 Series: Concepts and Architecture