HP XP Auto LUN Software - Manual (Page 12)

12 Auto LUN XP for the XP1024/XP128
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 XP1024/XP128 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 XP1024/XP128
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.
Estimating usage rates
The estimate function calculates expected usage of source and target parity groups after a proposed
volume migration. The estimate function uses subsystem usage data collected by the monitor function, HDD
performance characteristics, and RAID level to estimate expected usage rates. The automatic and manual
migration functions use these estimated values to verify proposed migrations.
For each proposed migration operation, Auto LUN XP automatically estimates expected usage rates for
source and target parity groups. The estimate function calculates expected results of a proposed volume
migration based on XP1024/XP128 monitor data collected during the user-specified monitor data term.
The estimate function considers RAID level and HDD type when estimating expected usage rates (RAID-1
and RAID-5 have different access characteristics).
The estimate function is a critical component of the auto migration function. The estimate function calculates
expected parity group usage for source and target parity groups, and the auto migration function uses
these estimates to verify proposed migrations. If any condition prevents Auto LUN XP from estimating an
expected usage rate (for example, invalid monitor data), the auto migration function will not schedule the
migration operation.
For manual migration operations, when you select the source volume, Auto LUN XP displays expected
usage rates for the source parity group, so you can see the predicted effect of migrating the selected
volume out of its group. When you select the target volume, Auto LUN XP displays expected usage rates for
the target parity group, so you can see the predicted effect of adding the selected source volume to the
selected parity group.