HP StorageWorks Auto LUN XP user guide for the XP10000/XP12000 (December 2005)

Auto LUN XP user guide for the XP10000/XP12000 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.
From an open-system host, you can also use RAID Manager command to perform manual volume
migration. To use RAID Manager to perform Auto LUN XP migration, install Auto LUN XP on the
XP10000/XP12000. For more information, see ”Using RAID Manager for manual Auto LUN XP
migrations” on page 38.
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 XP10000/XP12000 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 XP10000/XP12000, 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
XP10000/XP12000. 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.