Host
Host
Host
Backup System
Backup System
Intermediate device
Stop applications
Backup all data
Restore data
Restart
using new copy
Figure 15-5 Migration using backup and restore
The major disadvantage is again the disruptiveness. The applications that write to the data to be migrated must be stopped for the whole migration process. Backup and restore to and from tape usually takes longer than direct copy from disk to disk. The duration of the disruption can be reduced somewhat by using incremental backups.
15.2.2 Subsystem-based data migration
The DS6000 provides remote copy functionality, which also can be used to migrate data:
IBM TotalStorage Metro Mirror, formerly known as PPRC, for distances up to 300km
IBM TotalStorage Global Copy, formerly known as PPRC Extended Distance, for longer distances
A combination of Metro Mirror and Global Copy with an intermediate device in certain cases
These methods are host system agnostic and can therefore be used with only minimum system administrator attention. They also do not add any additional CPU load to the host systems, and they don't require the host system to be connected to both storage systems at the same time.
The necessary disruption is minimal. The initial copy is started during normal operation. Once it is complete, the target is kept
Important: The source storage system must be removed from the host completely, not only physically, but also logically, including all configuration data.
However, the copy functions do not allow for the consolidation of smaller volumes into larger ones, since they are not aware of the structure of the data.
Chapter 15. Data migration in the open systems environment | 295 |
