HP XP P9500 Storage - Manual (Page 7)

When to use manual volume migration
In the following scenarios, you must perform a manual migration plan instead of an Auto Migration
plan:
•
To analyze processor and access path usage
•
To migrate external volumes
•
To migrate Thin Provisioning or Thin Provisioning Z virtual volumes
•
To run RAID Manager commands on open-system and mainframe volumes from an open-system
host
To perform volume migration by RAID Manager, Auto LUN should be installed on the storage
system.
Automatic volume migration
Automatic volume migration allows you to automate the creation and execution of migration plans.
If you automate the creation and execution of migration plans, you do not need to analyze the
usage rates of storage system resources or the speed of hard disk drives. These tasks are performed
automatically by Auto LUN at a specified interval and time.
Auto migration plans are performed to balance the load of I/O activity in each HDD class and
across parity groups (groups of disks with similar speeds) within the same HDD class. The fastest
parity groups belong to class A. The maximum disk usage rate is specified for each HDD class in
the P9500 storage system. The maximum disk usage rate for an HDD class applies to all parity
groups within that class. When a parity group exceeds the threshold, the Auto Migration function
will initiate one of the following two plans:
•
Migrate one or more volumes in this parity group to another parity group in a higher HDD
class
•
Migrate one or more volumes in this parity group to a parity group with lower utilization in
the same HDD class
Auto LUN does not perform an Auto Migration operation which might result in the target parity
group exceeding the maximum disk usage rate.
NOTE: The default maximum disk usage rates are rough estimates only, and may not provide
the best results.
By default, each HDD class is assigned a certain limit on disk usage rate. Disk usage rate limit
affects Auto Migration performance. If the disk usage rate limit for one class is high, many volumes
might be migrated to parity groups in that class. If the disk usage rate limit for one class is low,
fewer volumes might be migrated to parity groups in that class. If necessary, you can change the
disk usage rate limit for an HDD class.
The following figure illustrates how the Auto Migration function identifies parity groups that exceed
the disk usage rate limit, and then selects high-usage volumes in these parity groups as the source
volumes to be migrated to a parity group in a higher HDD class, or to another parity group in the
same HDD class with lower utilization.
When to use manual volume migration 7