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336 DS8000 Series: Concepts and Architecture
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 16-2 outlines the process.
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.
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.
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.
Host
Copy all data
Stop applications
Host
Restart
using new copy