HP XP P9000 Auto LUN Software - Manual (Page 6)

volume to complete the migration. During the migration, the source volume remains available for
read and write operations.
The volume migration copy operation copies the content of the source volume to the target volume
cylinder by cylinder (24 tracks at a time, not including the diagnostic and unassigned alternate
tracks). If the source volume is updated by write operations during the copy operation, the updates
will be recorded on the cylinder map of a volume. If there are differential data created by the
update, the differential data are copied from the source volume to the target volume. This process
is repeated until all differential data on the source volume is copied. The following figure illustrates
the data flow during a manual migration operation.
Figure 1 Data flow during an Auto LUN operation
There is an upper limit to the number of times a copy operation is executed, and the limit depends
on the capacity of the source volume. The limit increases as the capacity of the source volume
increases. When differential data still exists after copy operations are repeated to the upper limit,
the migration fails. Before attempting the migration again, the workload between the host and the
storage system should be adequately reduced, preferably to a value below 50 IOPS (input/output
operations per second).
Once the volumes are fully synchronized (that is, there is no differential data on the source volume),
the XP P9500 storage system completes the migration by swapping the Reserve attribute (from
target volume to source volume) and redirecting host access to the target volume. The status of the
target volume becomes normal, and the status of the source volume becomes reserved. Auto LUN
performs all migration operations synchronously (that is, one migration at a time). The following
figure illustrates the state of the volumes after a manual migration operation.
Figure 2 Data flow after an Auto LUN operation
Immediately after the source volume and target volume are swapped (that is, the migration is
complete), the RAID level before the migration might be displayed, or an internal error might occur
in the storage system. If this occurs, try to resolve the issue by updating the display of the window.
6 Overview of Auto LUN