IBM DS8000 Online copy and synchronization with rsync, Migration using volume management software

This method also requires the disruption of applications writing to the data for the complete process.

Online copy and synchronization with rsync

rsync is an open source tool that is available for all major open system platforms, including Windows and Novell Netware.

Its original purpose is the remote mirroring of file systems with as few network requirements as possible. Once the initial copy is done, it keeps the mirror up to date by only copying changes. Additionally, the incremental copies are compressed.

rsync can also be used for local mirroring and therefore for data migration. It allows you to copy the data while applications are writing to it and thus minimizes the disruption. As for the normal copy commands, rsync works on file systems only. It also allows consolidation. Figure 16-3shows the steps required.

Host

Host

Host

Initial Copy

Incremental updates

Stop applications

Final synchronization

Restart

using new copy

Figure 16-3 Data migration with rsync

You set up the initial copy during normal operation, allowing enough time for the copy to complete before the planned switch to the new storage (cut over time). Once the initial copy is complete, you keep it up to date with incremental rsync runs, for instance once a day, during off-peak hours. At the cut over time, you stop the applications using the data, let rsnyc do a final synchronization, and restart the applications using the migrated data. The duration of the disruption depends only on the amount of data that has changed since the last re-synchronization.

More information about rsync can be found on the rsync project home page:

http://samba.org/rsync/

Migration using volume management software

Logical Volume Managers (LVMs) are available for all open systems (for Windows it is called Disk Manager). The LVM creates a layer of storage virtualization within the operating system. The most basic functionality every LVM provides is to:

￿Extend logical volumes across several physical disks

￿Stripe data across several physical disks to enhance performance

Chapter 16. Data migration in the open systems environment 337