HP (Hewlett-Packard) XP12000 User Manual

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Figure 2

Data Flow after an Auto LUN XP operation

NOTE:

Immediately after a source volume and a target volume replace each other, RAID level before the 

replacement might be displayed or an internal error might occur in the disk array. In this case, select 

Refresh to update the display.

Estimating usage rates

The estimate function calculates expected usage of source and target parity groups after a proposed 

volume migration. The estimate function uses subsystem usage data collected by the monitor function, HDD 

performance characteristics, and RAID level to estimate expected usage rates. The automatic and manual 

migration functions use these estimated values to verify proposed migrations.
For each proposed migration operation, Auto LUN XP automatically estimates expected usage rates for 

source and target parity groups. The estimate function calculates expected results of a proposed volume 

migration based on XP12000/XP10000 monitor data collected during the user-specified monitor data 

term. The estimate function considers RAID level and HDD type when estimating expected usage rates 

(RAID-1 and RAID-5 have different access characteristics).
The estimate function is a critical component of the auto migration function. The estimate function calculates 

expected parity group usage for source and target parity groups, and the auto migration function uses 

these estimates to verify proposed migrations. If any condition prevents Auto LUN XP from estimating an 

expected usage rate (for example, invalid monitor data), the auto migration function will not schedule the 

migration operation.
For manual migration operations, when you select the source volume, Auto LUN XP displays expected 

usage rates for the source parity group, so you can see the predicted effect of migrating the selected 

volume out of its group. When you select the target volume, Auto LUN XP displays expected usage rates for 

the target parity group, so you can see the predicted effect of adding the selected source volume to the 

selected parity group.
Auto LUN XP does not estimate processor or access path usage. You can use Auto LUN XP migration 

operations to improve DKP and DRR usage, but cannot use them to address CHP or access path usage.
Perform Auto LUN XP migration only when you expect a large improvement in disk array performance. 

Auto LUN XP migration might not provide significant improvement if parity group or volume usage varies 

only slightly or if overall DKP or DRR usage is relatively high. Also keep in mind that disk array tuning 

operations might improve performance in one area while decreasing performance in another. For 

example, suppose parity groups A and B have average usage values of 20% and 90%, respectively. Auto 

LUN XP estimates that if one logical volume is migrated from parity group B to parity group A, the usage 

values will become 55% and 55%. If you perform this migration operation, I/O response time for parity