HP XP Auto LUN Software - Manual (Page 13)

Auto LUN XP user guide for the XP1024/XP128 13
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
group B will probably decrease and I/O response time for parity group A might increase, while the overall
throughput might increase or decrease.
Automatic migration
Auto migration is the primary tuning method for disk arrays. Auto migration analyzes data and executes
migration plans automatically based on user-specified parameters. Use Auto LUN XP to schedule auto
migration operations, select data to be analyzed, and specify maximum time and performance impact of
auto migration operations. Auto LUN XP displays a detailed log of auto migration activities.
Auto migration operations are based on the following major parameters:
• Hierarchy of parity groups. Auto LUN XP arranges parity groups in the XP1024/XP128 in a hierarchy
based on HDD type, and assigns each parity group to a class based on performance of its HDD type.
Classes are ordered from highest performance drive (class A) to lowest performance drive (class B, C,
or higher depending on number of HDD types available). The auto migration function uses this
hierarchy to identify target volumes for auto migration operations.
The auto migration function can also specify “fixed” parity groups that are excluded from auto
migration operations.
• Maximum disk usage. The auto migration function specifies the maximum disk usage rate for each
HDD class in the XP1024/XP128, and uses these limits to identify source volumes for auto migration
operations.
You must identify and specify disk usage limits for your environment. When you use the same maximum
disk usage rate for all HDD classes, HDD performance is the only factor used in determining auto
migration plans. When you specify different usage limits for HDD classes, you can bias the auto
migration function to favor (or avoid) certain HDD types. Migrating high-usage volumes to higher HDD
classes should significantly improve host access to volumes, which can also have a large effect on disk
array performance.
The auto migration function also specifies the maximum disk usage rate during auto migration
operations, so you can control the impact of Auto LUN XP copy operations on disk array performance.
If source or target parity group usage exceeds the specified limit during migration, the auto migration
operation is canceled.
Do not perform manual migration operations while the auto migration function is active. Always turn off the
auto migration function and cancel any existing auto migration plan before performing manual migration
operations.
Storage management by maximum disk usage
Use the auto migration function to specify maximum usage rate for each HDD class in an XP1024/XP128.
When a parity group exceeds this limit, the auto migration function makes a plan to migrate one or more
volumes in this parity group to a parity group in a higher HDD class or to a parity group in the same HDD
class with lower usage.
This storage tuning method addresses and can eliminate disk drive activity bottlenecks. Auto LUN XP uses
its estimated usage rates to verify each proposed auto migration, and will not perform a migration
operation that might result in a target parity group exceeding the user-specified maximum disk usage rate.
The auto migration function identifies parity groups that exceed the user-specified usage limit, and selects
high-usage volumes as source volumes to be migrated to parity groups in higher HDD classes or to other
parity groups in the same HDD class with lower usage.