HP StorageWorks XP Remote Web Console Software - Manual (Page 12)

12 Auto LUN XP for the XP12000/XP10000
Reserve volumes
The reserve volume function reserves target volumes for automatic and manual migration operations. After
you reserve a number of target volumes, Auto LUN XP maintains this number of reserved volumes by
swapping the reserve attribute after each migration operation (following the migration operation, the
original source volume becomes a reserved volume).
Volume migration
Auto LUN XP volume migration operations consist of two steps:
• Copy the data on the Auto LUN XP source volume to the Auto LUN XP target volume
• Transfer host access to the target volume to complete the migration
The Auto LUN XP source volume can be online to hosts during migration. The target volume is reserved
prior to migration to prevent host access during migration. The source and target volumes can be anywhere
in the disk array.
The Auto LUN XP copy operation copies the entire contents of the source volume to the target volume. If
write I/Os update the source volume during the copy operation, the XP12000/XP10000 uses a cylinder
map to track updates and performs additional copy operations after the initial copy is complete to
duplicate the updates at the target volume.
When volumes are fully synchronized (no differential data on source volume), the XP12000/XP10000
completes the migration by swapping the reserve attribute (target becomes normal and source becomes
reserved) and redirecting host access to the target volume. Auto LUN XP performs all migration operations
sequentially (one volume migration at a time).
Typical copy times for open system volumes (with no other I/O activity) are:
• OPEN-3: 1.5 minutes
• OPEN-8/9: 4.5 minutes
• OPEN-E: 9 minutes
• OPEN-V: variable
For automatic and manual migration operations, Auto LUN XP checks the current write pending rate. If the
write pending rate is higher than 60%, Auto LUN XP cancels the migration. For auto migration, Auto LUN
XP also checks current disk usage of source volumes and source and target parity groups. If current disk
usage is higher than the user-specified maximum for auto migration, Auto LUN XP cancels the migration.
Figure 1 Data Flow during an Auto LUN XP Operation