HP StorageWorks XP Remote Web Console Software - Manual (Page 14)

class or to a parity group in the same HDD class with lower utilization. This storage-tuning method
addresses and can eliminate bottlenecks in hard disk drive activity and also provides load balancing
of hard disk drive usage. XP Auto LUN uses the estimated usage rates to verify each proposed
auto migration, and will not perform a migration operation which might result in a target parity
group exceeding the user-specified maximum disk usage rate.
NOTE: The default maximum usage values are rough estimates only and may not provide the
best results.
Figure 8 (page 14) illustrates how the auto migration function identifies parity groups that exceed
the user-specified usage limit, and then selects the high-usage volumes as the source volumes to
be migrated to parity groups in higher HDD classes or to other parity groups in the same HDD
class with lower utilization.
Figure 8 Migrating to Improve Disk Usage
When the parity groups in the highest HDD classes have run out of reserved volumes (are empty),
XP Auto LUN automatically migrates low-usage volumes from higher HDD class groups to lower
HDD class groups to maintain available reserve volumes.
Figure 9 Keeping Reserve Volumes in the Highest HDD Class Available
As explained previously, the auto migration function can move a high-usage volume to a higher
HDD class group, forcing a low-usage volume out of that HDD class group. To move one volume
into a different HDD class group, and then force another volume out of that class group, the auto
migration function requires a minimum of 5% difference in estimated disk usage between the two
volumes. If the difference in disk usage is less than 5%, this migration is considered an ineffective
strategy, and the volume is not moved.
14 About XP Auto LUN Operations