HP XP Racks - Manual (Page 5)

1 Overview of Auto LUN
This is an overview of Auto LUN.
Overview of Auto LUN
Auto LUN is used to optimize your data storage by balancing resource utilization and resolving
bottlenecks of system activity on the storage system. If heavy input/output (I/O) activity occurs on
a specific data drive or disk processor, the host might suffer from slower response times. To avoid
this situation, Auto LUN lets you migrate high-usage volumes to a low-usage data drive or a fast
data drive.
Migrating volumes with Auto LUN is completely non-disruptive as the data being migrated can
remain online to all hosts for read and write operations throughout the entire migration process.
The system administrator specifies the source volume and the target volume, and then executes the
migration plan.
Limitations of Auto LUN
You should keep in mind that Auto LUN operations can improve performance in one area while
decreasing performance in another. Consider the following scenario:
•
Parity Group A has an average usage value of 20%
•
Parity Group B has an average usage value of 90%
Through Auto LUN, it is estimated that if one volume from Parity Group B is migrated to Parity
Group A, the usage values of both parity groups become 55%. In this scenario, the I/O response
time for Parity Group B will most likely decrease, while the I/O response time for Parity Group A
will most likely increase. Overall, the throughput may increase or decrease.
Auto LUN should only be performed when you can expect a large improvement in storage system
performance. Auto LUN operations may not provide significant improvement for cases in which
parity group or volume usage varies only slightly, or for cases in which the overall MP or DRR
usages is relatively high.
When an error condition exists in the XP7 storage system, resource usage can increase or become
unbalanced. Do not use data collected during an error condition as the basis for planning Auto
LUN operations.
Source and target volumes
The Auto LUN source volume is the volume whose data will be migrated, and this data is migrated
to the Auto LUN target volume. Theoretically, the source and target volumes can be located
anywhere in the storage system, however, there are some restrictions for selecting source and
target volumes in migration. See
“Requirements” (page 8) for more information on requirements
and restrictions when selecting source and target volumes.
Volume migration
In a volume migration operation, the data on the source volume is copied to a target volume. Once
all data is copied to the target volume, host access is transferred to the target 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
Overview of Auto LUN 5